This chapter examines the architectural development of early Christian churches, focusing on their transformation from modest worship spaces into monumental basilicas and centrally planned buildings in Late Antiquity. Drawing on archaeological findings, architectural studies, historical texts and artistic analyses, it traces the evolution of church architecture from the fourth to the seventh century. It argues that early Christian churches did not develop in isolation but were heavily influenced by existing Roman architectural traditions, pointing out that the standard basilica model, with its central nave, aisles and apse, was adapted from Roman civic buildings, while centrally planned churches were inspired by imperial mausolea. The chapter also explores regional variations, such as the preference for polygonal apses in Constantinople and straight-ended churches in North Africa and the Levant, demonstrating how local traditions shaped Christian architecture. A key argument is that church architecture was not only functional but also symbolic, reinforcing Christian identity and imperial authority. The use of precious materials, elaborate mosaics and grand designs reflected the growing prestige of Christianity. The chapter also highlights the influence of emperors, particularly Constantine and Justinian, in shaping the architectural landscape of the early church, setting a precedent for later developments in Byzantine and Western medieval architecture.