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Thanks to Wikipedia, we now know the purpose of all the treasuries at Delphi...

From the entrance of the site, continuing up the slope almost to the temple itself, are a large number of votive statues, and numerous treasuries. These were built by the various Greek city states — those overseas as well as those on the mainland — to commemorate victories and to thank the oracle for her advice, which was thought to have contributed to those victories. They are called "treasuries" because they held the offerings made to Apollo; these were frequently a "tithe" or tenth of the spoils of a battle. The most impressive is the now-restored Athenian Treasury, built to commemorate the Athenians' victory at the Battle of Salamis. According to Pausanias, the Athenians had previously been given the advice by the oracle to put their faith in their "wooden walls" — taking this advice to mean their navy, they won a famous battle at Salamis. Several of the treasuries can be identified, among them the Siphnian Treasury, dedicated by the city of Siphnos whose citizens gave a tithe of the yield from their gold mines until the mines came to an abrupt end when the sea flooded the workings.

As a result of these treasuries, through the protection of the Amphictyonic League, Delphi came to function as the de-facto Central Bank of Ancient Greece. It was the abuse of these treasuries by Philip of Macedon and the later sacking of the Treasuries, first by the Celts, and later by Sulla, the Roman Dictator, that led to the eclipse of Greek civilization and the eventual growth of Rome.

http://en.wikipedia.org/wiki/Delphi