The churches of St John and St Mary at Ephesos, 'Building D' at Sardis, St John at Philadelphia, and the basilicas of Hierapolis illustrate the development of vaulted construction on the west coast of Asia Minor between the 5th and the 7th century AD. These churches, due to their dilapidated condition, constitute ideal sources of information about the materials and construction techniques employed in some of the most important building programs of the early Byzantine Empire. The ruined state of the monuments and the lack of written records have hindered attempts to reconstruct their original forms. Although the surviving load-bearing elements of most of the churches have been very well documented, the potential of their remains to offer information about the nature of vaults has not yet been fully appreciated. As a result, the vaulting practices of west Asia Minor remain enigmatic, though they clearly influenced the early development of Byzantine church architecture. The constructional analysis of these churches, along with the reconstruction of their vaults, constitutes the main thrust of the present study. The author's new documentation of their structural fabric, carried out in the field during 2007 and 2008, concentrates on the recording of a series of unexplored vault fragments and construction details. The graphic investigation of this evidence, aided by interpretation on the basis of formal comparisons, leads to reasoned revised reconstructions of each church. The resulting reconstruction drawings form the basis for the exploration of some of the most interesting early Byzantine vaulting patterns. Continuing efforts initiated by A. Choisy more than a century ago, this leads to a new typology of vault structures for the region. The latter embraces the structural tissue of vaults, and, thus, hopes to go beyond classifications based solely on geometrical forms, which are too restrictive to respond to the wide variety of solutions found in the region. This book reveals the diversity, elegance and sophistication that characterize some of the most important early Byzantine churches. The analytical study of these monuments highlights the role of the cities of west Asia Minor as centres for experimentation in the field of vaulted construction during the first centuries of the Byzantine period.