From Project Athinai
A walled triangular sanctuary was erected on a sacred spot at the southwest corner of the Agora around 435 BC. The low walls were made of polygonal limestone masonry. An inscription on a marble post set against the north wall (at its east end) indicated "Of the Sanctuary".
American School of Classical Studies at Athens; The Athenian Agora: A Guide to the Excavation and Museum, 1990