This study examines the introduction of round-pier structures (composed of round piers with vault shafts standing on
the capitals and hitherto employed only in ambulatories) into naves of Early Gothic churches. The findings revealed
that the introduction assumed either one of the following two ways: churches without transepts introduced round-pier
structures alternately with compound-pier ones, whereas churches with transepts introduced round-pier structures
continuously only in the choirs. For the purpose of this study, all churches with ambulatories were selected among the
12th-century Île-de-France churches that were accompanied with round-pier structures. Further, the construction dates
of the churches were compared.