Before the Athenian treasury was stored in the Parthenon, it was kept in the opisthodomos, or back room of the old temple to Athena Polias. When it burned, the treasury was moved to the Parthenon and the old site used to build the Erechteon, effectively obscuring the remains of the original site. In this paper William Dinsmoor, a historian of architecture and one of the scholars involved in the rebuilding of the Acropolis in the early 20th century, here uses a wide variety of evidence to set a date for this burning. This piece is of interest to anyone wishing to develop a better appreciation for the Athenian Acropolis and its history as well as those wishing to see this master of reconstruction apply his mind to a difficult problem in archeology.