 Wilhelm Dörpfeld assumed that the original structure was a double temple "in antis", dating to about 570 BC, lengthened and broadened by the addition of the "peristasis" under Peisistratus, between 529 and 520 BC.This idea led to a subdivision of the foundations into an inner smaller structure known as "H-Architektur" and assumed to be the oldest part of the building, followed by a structure still described as the "Old Temple of Athena", including the inner "H-Architektur" as well as the external "peristasis".The reconstruction of the temple's architectural history has remained controversial until recently.