A Double church, or twin church, is a church design found in Byzantine architecture. The double church design of the Üçayak Byzantine Church features double naves standing side by side and separated by a common wall. The twin church design at Üçayak has two naves each with a separate semi-circular apse. Each apse includes a rectangular bay in front of it.
^ abToivanen, Hanna-Riitta (2001). "Byzantine Church at Üçayak (Kirşehir, Cappadocia)". Encyclopaedia of the Hellenic World, Asia Minor. Close to the ruined church there was a spring of water, but no material remains have been found, which means, that this church was built originally in a completely isolated and remote place.
^ abMihaljević, Marina (2014). "Üçayak: a forgotten Byzantine church". Byzantinische Zeitschrift. 2 (107): 725–754, pl. I–V. Regarding the possible function of the twin-church of Üçayak, this article argues for the burial and commemorative functions, which often motivated the double arrangement in Cappadocian rock-cut churches. ... The edifice is, namely, arranged as a twin church, which makes it relatively uncommon within the context of Byzantine architecture (fig. 1).