Greek-cross or cross-in-square plan was the dominant architectural scheme of the Byzantine churches during the middle and late periods of the empire. As can be deduced from the name, a Greek-cross plan church had a square naos with a cross-shaped internal structure topped by a dome. The first example of this plan probably dates from the late 8th century, and it was common throughout the Orthodox settlements. Here are some examples of the well-preserved Greek-cross plan Byzantine churches most of which later became a mosque under Ottoman rule.
Myrelaion Church (Bodrum Mosque) in Istanbul, Turkey
Today known as the Bodrum Mosque, the church of the Myrelaion Monastery dates from around 920. It was built on top of a Roman rotunda next to the palace of Byzantine Admiral Romanus Lecapenus. It functioned as a nunnery until the Ottoman conquered Constantinople in 1453. Later the Grand Vizier Mesih Pasa converted the church into a mosque circa 1500. The Myrelaion Church is a great example of a Greek cross-plan church which is discernible from the four cross vaults around a dome, creating a Greek cross shape. The church also has a highly symmetrical exterior emphasizing its square form as well as the central dome.
Monastery of Lips (Fenari Isa Mosque) in Istanbul
Founded in 907, there is little information about the use of the Monastery of Lips until the late 13th century when Theodora Palaiologina restored the structure. She added a second church to the pre-existing tenth-century South church and had a hospital built in the monastery. Then, Theodora instituted a nunnery in the north church. By the end of the 15th century, Ali Efendi of the Fenari family converted the south church into a mosque.
The monastery went through several changes after a fire in the 17th century. The columns in the naves, as well as four principal columnar supports, were transformed into pointed arches. Moreover, both domes were rebuilt, and a minaret was erected at the southwestern corner of the narthex. Meanwhile, the north church had become a tekke (a dervish lodge) by the end of the century.
Agios Stefanos Church (today known as Tirilye Fatih Mosque) in Bursa, Turkey
The 8th-century Agios Stefanos church is one of the earliest examples of Greek-cross plan Byzantine churches. It later became a mosque in the 16th century with the name Fatih Mosque. The structure served once more as a church during the Greek invasion between 1920-22, then returned to its previous status after the invasion.
Theotokos Kyriotissa Church (Kalenderhane Mosque) in Istanbul
The Theotokos Kyriotissa Church, now Kalenderhane Mosque, mostly dates to the 12th century but includes some earlier structures, the earliest one being a 4th-5th century bath. The structure also contains a 6th-century Byzantine basilica. The main church was built around 1200 in Greek cross-plan topped by a dome. Mehmed II assigned the church to the Kalenderi sect of the Dervish after the conquest of Constantinople. The structure finally became a mosque in the 18th century.
Hosios Loukas Monastery in Boeotia, Greece
Founded in the early 10th century, the Hosios Loukas Monastery lies on the west slope of Mount Helikon. The small church in the monastery is the earliest example of a Greek plan church in the country.
Monastery of the Pantokrator (Zeyrek Mosque) in Istanbul, Turkey
Built between 1118 and 1136, the Monastery of Pantokrator was one of the most prominent imperial complexes in Constantinople after the rule of Justinian. Both the south and the north churches are in Greek cross plan, and the middle part is the imperial chapel. Soon after the conquest of Constantinople, Mehmed II turned the monastery into a madrasa with Zeyrek Molla as its first müderris (similar to a professor). After adding a minbar and a mihrab and plastering the walls, the structure also became a mosque.