Khoca Mimar Sinan Ağa (Ottoman Turkish: خواجه معمار سنان آغا; Modern Turkish: Mimar Sinan) (c. 1490 - 1578) was the chief Ottoman architect and civil engineer for sultans Suleiman I, Selim II, and Murad III. He was responsible for the construction of more than three hundred major structures, and other more modest projects, such as his Koran schools (sibyan mektebs).

Trained as a military engineer, he rose through the ranks to become first an officer and finally a Janissary commander, with the honorific title of ağa. He learned his architectural and engineering skills while on campaign with the Janissaries, becoming expert at constructing fortifications of all kinds, as well as military infrastructure, such as roads, bridges and aqueducts. At about the age of fifty, he was appointed as chief royal architect, applying the technical skills he had acquired in the army to the "creation of fine religious buildings" and civic structures of all kinds. He remained in post for almost fifty years. His masterpiece is the Selimiye Mosque in Edirne, although his most famous work is the Suleiman Mosque in Istanbul. He headed an extensive governmental department and trained many assistants who, in turn, distinguished themselves, including Sedefhar Mehmet Ağa, architect of the Sultan Ahmed Mosque. He is considered the greatest architect of the classical period of Ottoman architecture, and has been compared to Michelangelo, his contemporary in the West. Michelangelo and his plans for St. Peter's Basilica in Rome were well known in Istanbul, since Leonardo da Vinci and he had been invited, in 1502 and 1505 respectively, by the Sublime Porte to submit plans for a bridge spanning the Golden Horn.

According to contemporary biographer, Mustafa Sâi Çelebi, Sinan was born with the name Joseph as an Armenian or Rûm (Greek) Christian in 1489, in a small town called Ağırnas (present day Mimarsinanköy) near the city of Kayseri in Anatolia (as stated in an order by Sultan Selim II.) One argument that lends credence to his Armenian background is a letter he wrote to Selim II in 1573, asking the Sultan to spare his family from the general exile of Kayseri's Armenian community. Little is known of his family background, apart from the fact that his father was a stone mason and carpenter, and Sinan (Joseph) grew up helping him in these businesses. There are three brief records in the library of the Topkapı Palace, dictated by Sinan to his friend Mustafa Sâi Çelebi. In these manuscripts, Sinan divulges some details of his youth and military career. According to these documents, Sinan was the son of "Abdülmenan" (the anonym of Christian fathers whose sons were Muslim converts), but this name is also given as "Abdullah" (عبد الله, which means Servant of God in Arabic) and "Hristo" (Χρήστος, common Greek name, meaning Christ.)

In 1512, Sinan was conscripted into Ottoman service via the devşirme system. He went to Istanbul as a recruit of the Janissary Corps, and was converted to Islam. Since he was over twenty-one years old, he was not admitted to the imperial Enderun School in the Topkapı Palace but was sent instead to an auxiliary school. Some records claim that he might have served the Grand Vizier İbrahim Paşa as a novice of the Ibrahim Pasha School. Possibly, he was given the Islamic name Sinan there. He initially learned carpentry and mathematics but through his intellectual qualities and ambitions, he soon assisted the leading architects and got his training as an architect.

During the next six years, he also trained to be a Janissary officer (acemioğlan). He possibly joined Selim I in his last military campaign, Rhodes according to some sources, but when the Sultan died, this project ended. Two years later he witnessed the conquest of Belgrade. He was present, as a member of the Household Cavalry, in the Battle of Mohács, led by the new sultan Suleiman the Magnificent. He was promoted to captain of the Royal Guard and then given command of the Infantry Cadet Corps. He was later stationed in Austria, where he commanded the 62nd Orta of the Rifle Corps. He became a master of archery, while at the same time, as an architect, learning the weak points of structures when gunning them down. In 1535 he participated in the Baghdad campaign as a commanding officer of the Royal Guard. In 1537 he went on expedition to Corfu and Apulia and finally to Moldavia.

During all these campaigns he had proven himself a trained engineer and an able architect. When the Ottoman army captured Cairo, Sinan was promoted to chief architect and was given the privilege of tearing down any buildings in the captured city that were not according to the city plan. During the campaign in the East, he assisted in the building of defences and bridges, such as a bridge across the Danube. He converted churches into mosques. During the Persian campaign in 1535 he built ships for the army and the artillery to cross Lake Van. For this he was given the title Haseki'i, Sergeant-at-Arms in the body guard of the Sultan, a rank equivalent to that of the Janissary Ağa.

When Chelebi Lütfi Pasha became Grand Vizier in 1539, he appointed Sinan, who had previously served under his command, Architect of the Abode of Felicity. This was the start of a remarkable career. It was his task to supervise the constructions and the flow of supplies within the Ottoman empire. He was also responsible for the design and construction of public works, such as roads, waterworks and bridges. Through the years he transformed his office into that of Architect of the Empire, an elaborate government department, with greater powers than his supervising minister. He became the head of a whole Corps of Court Architects, training a team of assistants, deputies and pupils. His training as an army engineer gave Sinan rather an empirical approach to architecture than a theoretical one. But the same can be said of the great Western Renaissance architects, such as Brunelleschi and Michelangelo.

Various sources state that Sinan was the architect of around 360 structures which included 84 mosques, 51 small mosques ("mescit"), 57 schools of theology ("medrese"), 7 schools for Koran reciters ("darülkurra"), 22 mausoleums ("türbe"), 17 Alm Houses ("imaret"), 3 hospitals ("darüşşifa"), 7 aqueducts and arches, 48 inns ("caravansary"), 35 palaces and mansions, 8 vaults and 46 baths. Sinan, who held the position of chief architect of the palace, which meant being the top manager of construction works of the Ottoman Empire, for nearly 50 years, worked with a large team of assistants consisting of architects and master builders.

The development and maturing stages of Sinan can be marked with three major works. The first two of these are in Istanbul - Shehzade Mosque which he calls his apprenticeship period work, Süleymaniye Mosque which is the work of his qualification stage, and Selimiye Mosque in Edirne the product of his master stage. Şehzade Mosque is the first of the grand mosques Sinan has created. Mihriman Sultan Mosque which is also known as the Üsküdar Quay Mosque was completed in the same year and has an original design with its main dome supported by three half domes. When Sinan reached the age of 70, he had completed the Süleymaniye Mosque and the Complex. This building, situated on one of the hills of Istanbul facing the Golden horn, and built in the name of Süleyman the Magnificent, is one of the symbolic monuments of the period. The diameter of the dome which exceeds 31 meters at Selimiye Mosque which Sinan completed when he was 80, is the most significant example of the level of achievement Sinan reached in architecture. Mimar Sinan has reached his artistic summit with the design, architecture, tile decorations, land stone workmanship displayed at Selimiye.

Another area of architecture where Sinan delivered unique projects are the mausoleums. Mausoleum of Şehzade Mehmed gets attention with its exterior decorations and sliced dome. Rüstem Paşa mausoleum is a very attractive structure in classical style. The mausoleum of Süleyman the Magnificent which is one of his interesting experimentations has an octagonal body and flat dome. Selim II Mausoleum with has a square plan and is one of the best examples of Turkish mausoleum architecture. Sinan's own mausoleum which is located at the north - east part of the Süleymaniye complex on the other hand, is a very plain structure.

Sinan, in the bridges he built, has masterfully combined art with functionalism. The largest of his work in this group is the nearly 635 meter long Büyükçekmece Bridge. Other significant examples are Ailivri Bridge, Lüleburgaz (Sokullu Mehmet Pasha) Bridge on Lüleburgaz River, Sinanlı Bridge over Ergene River and Drina Bridge which became the title of the famous novel of Yugoslav author İvo Andriç.

While Sinan was maintaining and improving the water supply system of Istanbul, he built arched aqueducts at several locations within the city. Mağlova Arch over Alibey River, which is 257 meters long, 35 meters high and displaying two layers of arches, is one of the best samples of its kind.

At the start of Sinan's career, Ottoman architecture was highly pragmatic. Buildings were repetitions of former types and were based on rudimentary plans. They were more an assembly of parts than a conception of a whole. An architect could sketch a plan for a new building and an assistant or foreman knew what to do, because novel ideas were avoided. Moreover, architects used an extravagant margin of safety in their designs, resulting in a wasteful use of material and labour. Sinan would gradually change all this. He was to transform established architectural practices, amplifying and transforming the traditions by adding innovations, trying to approach perfection. During these years he continued the traditional pattern of Ottoman architecture; but he gradually began exploring other possibilities, because, during his military career, he had had the opportunity to study the architectural monuments in the conquered cities of Europe and the Middle East.

His first attempt to build an important monument was the Hüsrev Pasha mosque and its double medresse in Aleppo, Syria. It was built in the winter of 1536 - 1537 between two army campaigns for his commander-in-chief and the governor of Aleppo. It was built in haste and this is demonstrated in the coarseness of execution and the crude decoration.

His first major commission as the royal architect was the construction of a modest Haseki Hürrem complex for Roxelana (Hürem Sultan), the wife of the sultan, Süleyman the Magnificent. He had to follow the plans drawn by his predecessors. Sinan retained the traditional arrangement of the available space without any innovations. Nevertheless it was already better built than the Aleppo mosque and it shows a certain elegance. However, it has suffered from many restorations.

In 1541, he started the construction of the mausoleum (türbe) of the Grand Admiral Hayreddin Barbarossa. It stands on the shore of Beşiktaş on the European part of Istanbul, at the site where his fleet used to assemble. Oddly enough, the admiral is not buried there, but in his türbe next to the Iskele mosque. This mausoleum has been severely neglected since then.

Mihrimah Sultana, the only daughter of Süleyman and wife of the Grand Vizier Rüstem Pasha gave Sinan the commission to build a mosque with medrese (college), an imaret (soup kitchen) and a sibyan mekteb (Qur'an school) in Üsküdar. The imaret no longer exists. This Iskele Mosque (or Jetty mosque) already shows several hallmarks of Sinan's mature style: a spacious, high-vaulted basement, slender minarets, single-domed baldacchino, flanked by three semi-domes ending in three exedrae and a broad double portico. The construction was finished in 1548. The construction of a double portico was not a first in Ottoman architecture, but it set a trend for country mosques and mosques of viziers in particular. Rüstem Pasha and Mihrimah required them later in their three mosques in Istanbul and in the Rüstem Pasha Mosque in Tekirdağ. The inner portico traditionally has stalactite capitals while the outer portico has capitals with chevron patterns (baklava).

When sultan Süleyman the Magnificent returned from another Balkan campaign, he received news that his heir to the throne Ṣehzade Mehmet had died at the age of twenty-two. In November 1543, not long after Sinan had started the construction of the Iskele Mosque, the sultan ordered Sinan to build a new major mosque with an adjoining complex in memory of his favourite son. This Şehzade Mosque would become larger and more ambitious than his previous ones. Architectural historians consider this mosque as Sinan's first masterpiece. Obsessed by the concept of a large central dome, Sinan turned to the plans of mosques such as the Fatih Pasha Mosque in Diyarbakır or the Piri Pasha Mosque in Hasköy. He must have visited both mosques during his Persian campaign. Sinan built a mosque with a central dome, this time with four equal half-domes. This superstructure is supported by four massive, but still elegant free-standing, octagonal, fluted piers and four piers incorporated in each lateral wall. In the corners, above roof level, four turrets serve as stabilizing anchors. This coherent concept already is markedly different from the additive plans of traditional Ottoman architecture. Sedefhar Mehmet Ağa would later copy the concept of fluted piers in his Sultan Ahmed Mosque in an attempt to lighten their appearance. Sinan, however, rejected this solution in his next mosques.

By 1550 Sultan Süleyman the Magnificent was at the height of his powers. Having built a mosque for his son, he felt it was time to construct his own imperial mosque, an enduring monument larger than all the others, to be built on a gently sloping hillside dominating the Golden Horn. Money was no problem, since he had accumulated a treasure from the loot of his campaigns in Europe and the Middle East. He gave the order to his royal architect Sinan to build a mosque, the Süleymaniye, surrounded by a külliye consisting of four colleges, a soup kitchen, a hospital, an asylum, a hamam, a caravanserai and a hospice for travellers (tabhane). Sinan, now heading a formidable department with a great number of assistants, finished this formidable task in seven years. Before Süleymaniye, no mosques had been built with half cubic roofs. He got the idea of half cubic roof design from the Hagia Sophia. Through this monumental achievement, Sinan emerged from the anonymity of his predecessors. Sinan must have known the ideas of the Renaissance architect Leone Battista Alberti (who in turn had studied De architectura by the Roman architect and engineer Vitruvius), since he too was concerned in building the ideal church, reflecting harmony through the perfection of geometry in architecture. But, contrary to his Western counterparts, Sinan was more interested in simplification than in enrichment. He tried to achieve the largest volume under a single central dome. The dome is based on the circle, the perfect geometrical figure representing, in an abstract way, a perfect God. Sinan used subtle geometric relationships, using multiples of two when calculating the ratios and the proportions of his buildings. However, in a later stage, he also used divisions of three or ratios of two to three when working out the width and the proportions of domes, such as the Sokollu Mehmet Pasha Mosque at Kadırga.

While he was fully occupied with the construction of the Süleymaniye, Sinan (or better the subordinates of his office under his supervision) drew the plans and gave definite instructions for many other constructions. But it is highly improbable that he supervised the construction of any of the provincial assignments.

Sinan built for the Grand Vizier Ibrahim Pasha a mosque and a funeral monument (türbe) at Silivrikapı (Istanbul) in 1551.

The next Grand Vizier Rüstem Pasha gave Sinan several more commissions. In 1550 Sinan built a large inn (han) in the Galata district of Istanbul. About ten years later another han in Edirne, and between 1544 and 1561 the Taṣ Han at Erzurum. He designed acaravanserai in Eregli and an octogal madrasah in Istanbul.

Between 1553 and 1555, Sinan built a Sinan Pasha Mosque at Beşiktaş, a smaller version of the Üç Şerefeli Mosque at Edirne, for the Grand Admiral Sinan Pasha. This proves again that Sinan had thoroughly studied the work of other architects, especially as he was responsible for the upkeep of these buildings. He copied the old form, pondered over the weaknesses in the construction and tried to solve this with his own solution. In 1554 Sinan used the form of the Sinan Pasha mosque again for the construction of the mosque for the next Grand Vizier Kara Ahmet Pasha in Istanbul, his first hexagonal mosque. By applying this hexagonal form, Sinan could reduce the side domes to half-domes and set them in the corners at an angle of 45 degrees. Clearly, Sinan must have appreciated this form, since he repeated it later in mosques such as the Sokollu Mehmed Pasha Mosque at Kadırga and the Atik Valide Mosque at Üsküdar.

In 1556 Sinan built the Haseki Hürrem Hamam, replacing the antique Baths of Zeuxippus still standing close to the Hagia Sophia. This would become one of the most beautiful hamams he ever constructed.

In 1559 he built the Cafer Ağa madrasah below the forecourt of the Hagia Sophia. In the same year he began the construction of a small mosque for Iskender Pasha at Kanlıka, beside the Bosphorus. This was one of the many minor and routine commissions the office of Sinan received over the years.

In 1561, when Rüstem Pasha died, Sinan began the construction of the Rüstem Pasha Mosque, as a memorial supervised by his widow Mihrimah Sultana. It is situated just below the Süleymaniye. This time the central form is octagonal, modelled on the monastery church of Saints Sergius and Bacchus, with four small semi-domes set in the corners. In the same year, Sinan built a funeral monument (türbe) for Rüstem Pasha in the garden of the Şehzade Mosque, decorated with the finest tiles Iznik could produce. Mihrimah Sultana, having doubled her wealth after the death of her husband, now wanted a mosque of her own. Sinan built for her the Mihrimah Camii at Edirnekapı (Edirne Gate), on the highest of the seven hills of Istanbul. He raised the mosque on a vaulted platform, accentuating its hilltop site. There is some speculation concerning the dates, until recently this was supposed to be between 1540 and 1540, but now it is generally accepted to be between 1562 and 1565. Sinan, concerned with grandeur, built a mosque in one of his most imaginative designs, using new support systems and lateral spaces to increase the area available for windows. He built a central dome of 37 m high and 20 m wide, supported by pendentives, on a square base with two lateral galleries, each with three cupolas. At each corner of this square stands a gigantic pier, connected with immense arches each with 15 large windows and four circular ones, flooding the interior with light. The style of this revolutionary building was as close to the Gothic style as Ottoman structure permits.

Between 1560 and 1566 Sinan built a mosque in Istanbul for Zal Mahmud Pasha on a hillside beyond Ayvansaray. Sinan certainly conceived the plans and partly supervised the construction, but left the building of lesser areas to less than competent hands, since Sinan and his most able assistants were about to begin his masterpiece, the Selimiye Mosque in Edirne. On the outside, the mosque rises high, with its east wall pierced by four tiers of windows. This gives the mosque an aspect of a palace or even a block of apartments. Inside, there are three broad galleries making the interior look compact. The heaviness of this structure makes the dome look unexpectedly lofty. These galleries look like a preliminary try-out for the galleries of the Selimiye Mosque.

In this late stage of his life, Sinan tried to create unified and sublimely elegant interiors. To achieve this, he eliminated all the unnecessary subsidiary spaces beyond the supporting piers of the central dome. This can be seen in the Sokollu Mehmet Paşa mosque in Istanbul (1571 – 1572) and in the Selimiye mosque in Edirne. In other buildings of his final period, Sinan experimented with spatial and mural treatments that were new in the classical Ottoman architecture.

According to him from his autobiography "Tezkiretü’l Bünyan", his masterpiece is the Selimiye Mosque in Edirne. Breaking free of the handicaps of traditional Ottoman architecture, this mosque marks the climax of Sinan's work and of all classical Ottoman architecture. While it was being built, the architect's saying of "You can never build a dome larger than the dome of Hagia Sophia and specially as Muslims" was his main motivation. When it was completed, Sinan claimed that it had the largest dome in the world, leaving Hagia Sophia behind. In fact, the dome height from the ground level was lower and the diameter barely larger (0.5 meters, approximately 2 feet) than the millennium-older Hagia Sophia. However, measured from its base the dome of Selimiye is higher. Sinan was more than 80 years old when the building was finished. In this mosque he finally realized his aim of creating the optimum, completely unified, domed interior : a triumph of space that dominates the interior. He used this time an octagonal central dome (31.28 m wide and 42 m high), supported by eight elephantine piers of marble and granite. These supports lack any capitals but have squinches or consoles at their summit, leading to the optical effect that the arches seem to grow integrally out of the piers. By placing the lateral galleries far away, he increased the three-dimensional effect. The many windows in the screen walls flood the interior with light. The buttressing semi-domes are set in the four corners of the square under the dome. The weight and the internal tensions are hidden, producing an airy and elegant effect rarely seen under a central dome. The four minarets (83 m high) at the corners of the prayer hall are the tallest in the Muslim world, accentuating the vertical posture of this mosque that already dominates the city.

He also designed the Taqiyya al-Sulaimaniyya khan and mosque in Damascus, still considered one of the city's most notable monuments, as well as the Banya Bashi Mosque in Sofia, Bulgaria, currently the only functioning mosque in the city. He has also built Mehmed Paša Sokolović Bridge in Višegrad across the Drina River in the east of Bosnia and Herzegovina which is now a UNESCO World Heritage Site.

At the start of his career as an architect, Sinan had to deal with an established, traditional domed architecture. His training as an army engineer led him to approach architecture from an empirical point of view, rather than from a theoretical one. He started to experiment with the design and engineering of single-domed and multiple-domed structures. He tried to obtain a new geometrical purity, a rationality and a spatial integrity in his structures and designs of mosques. Through all this, he demonstrated his creativity and his wish to create a clear, unified space. He started to develop a series of variations on the domes, surrounding them in different ways with semi-domes, piers, screen walls and different sets of galleries. His domes and arches are curved, but he avoided curvilinear elements in the rest of his design, transforming the circle of the dome into a rectangular, hexagonal or octagonal system. He tried to obtain a rational harmony between the exterior pyramidal composition of semi-domes, culminating in a single drumless dome, and the interior space where this central dome vertically integrates the space into a unified whole. His genius lies in the organization of this space and in the resolution of the tensions created by the design. He was an innovator in the use of decoration and motifs, merging them into the architectural forms as a whole. He accentuated the centre underneath the central dome by flooding it with light from the many windows. He incorporated his mosques in an efficient way into a complex (külliye), serving the needs of the community as an intellectual centre, a community centre and serving the social needs and the health problems of the faithful.

When Sinan died, the classical Ottoman architecture had reached its climax. No successor was gifted enough to better the design of the Selimiye mosque and to develop it further. His students retreated to earlier models, such as the Şehzade mosque. Invention faded away, and a decline set in.

During his tenure during 50 years of the post of imperial architect, Sinan is said to have constructed or supervised 476 buildings (196 of which still survive), according to the official list of his works, the Tazkirat-al-Abniya. He couldn't possibly have designed them all, but he relied on the skills of his office. He took credit and the responsibility for their work. For, as a janissary, and thus a slave of the sultan, his primary responsibility was to the sultan. In his spare time, he also designed buildings for the chief officials. He delegated to his assistants the construction of less important buildings in the provinces.

He died in 1588 and is buried in a tomb in Istanbul, a türbe of his own design, in the cemetery just outside the walls of the Süleymaniye Mosque to the north, across a street named Mimar Sinan Caddesi in his honour. He was buried near the tombs of his greatest patrons: Sultan Süleyman and the Sultana Haseki Hürrem, Suleiman's wife. His name is also given to: a crater on the planet Mercury and a Turkish state university, the Mimar Sinan University of Fine Arts in Istanbul.

Sinan's portrait was depicted on the reverse of the Turkish 10,000 lira banknotes of 1982 - 1995.