Minoan ceramics have been found in contexts of . The famous Aegina Treasure, now in the British Museum is estimated to date between 1700 and 1500 BC. The discovery on the island of a number of gold ornaments belonging to the last period of Mycenaean art suggests that Mycenaean culture existed in Aegina for some generations after the Dorian conquest of Argos and Lacedaemon. It is probable that the island was not Doricised before the 9th century BC. One of the earliest historical facts is its membership in the Amphictyony or League of Calauria, attested around the 8th century BC. This ostensibly religious league included—besides Aegina—Athens, the Minyan (Boeotian) Orchomenos, Troezen, Hermione, Nauplia, and Prasiae. It was probably an organisation of city-states that were still Mycenaean, for the purpose of suppressing piracy in the Aegean that began as a result of the decay of the naval supremacy of the Mycenaean princes. Aegina seems to have belonged to the Eretrian league during the Lelantine War; this, perhaps, may explain the war with Samos, a major member of the rival Chalcidian league during the reign of King Amphicrates (Herod. 59), i.e. not later than the earlier half of the 7th century BC. Its early history reveals that the maritime importance of the island dates back to pre-Dorian times. It is usually stated on the authority of Ephorus, that Pheidon of Argos established a mint in Aegina, the first city-state to issue coins in Europe, the Aeginetic stater. One stamped stater (having the mark of some authority in the form of a picture or words) can be seen in the Bibliothèque Nationale of Paris. It is an electrum stater of a turtle, an animal sacred to Aphrodite, struck at Aegina that dates from 700 BC. Therefore, it is thought that the Aeginetes, within 30 or 40 years of the invention of coinage in Asia Minor by the Ionian Greeks or the Lydians (c. 630 BC), might have been the ones to introduce coinage to the Western world. The fact that the Aeginetic standard of weights and measures (developed during the mid-7th century) was one of the two standards in general use in the Greek world (the other being the Euboic-Attic) is sufficient evidence of the early commercial importance of the island.