Two successive temples, built on the same foundations, are discussed in this detailed architectural history: an Archaic building built around 700 B.C. and a Classical 5th-century successor. Little is left visible at Isthmia of the temples that would have dominated the sanctuary, and, therefore, this study presents a painstaking exercise in detective work. This yields important results, such as an almost complete reconstruction of the Archaic roof, and a detailed investigation of the workings of the perirrhanterion (a basin for ablutions). Traces of color on the architectural fragments of the temple have been painstakingly recorded, and an appendix discusses the evidence for an unusual 32.04 cm foot being used as the basis for construction.