I'm referring to this temple in Egypt. It was destroyed in 410 BC and the Jewish community there requested it be rebuilt. In that letter they state that the temple pre-dates the Persian takeover of Egypt as it was spared by Cambyses even though he destroyed Egyptian temples. This is supported by a 2nd century BC document which claims that there were multiple waves of Jewish emigres into Egypt, beginning in 650 BC in support of the Egyptians campaign against Nubia (Elephantine Island is a fort on that border) but also those which are mentioned in the OT such as after the Babylonian invasions of Palestine. Hence the dating of the site is pre-Persian at the moment and requires evidence of it not being so to date it solely to the Persian period.
(the essay linked as a reference earlier in the thread covers most of this).