in 510 BC. In the early fifth century, Poseidonia's coins adopted the Achaean weight standard and the bull seen on Sybarite coins. A. J. Graham thinks it was plausible that the number of refugees was large enough for some kind of synoecism to have occurred between the Poseidonians and the Sybarites, possibly in the form of a sympolity. Poseidonia might have had a major share in a new foundation of Sybaris, which lasted from 452/1 BC until 446/5 BC. This is suggested by the great resemblance of the coins of Sybaris to those of Poseidonia during this period. Possibly a treaty of friendship between Sybaris, its allies, and the Serdaioi (an unknown people) dates to this new foundation, because Poseidonia was the guarantor of this treaty. Lucanian period It is not until the end of the fifth century BC that the city is mentioned, when according to Strabo, the city was conquered by the Lucanians. From the archaeological evidence it appears that the two cultures, Greek and Oscan, were able to thrive alongside one another. Many tomb paintings show horses and horse-racing, a passion of the Lucanian elites. Roman period and abandonment It became the Roman city of Paestum in 273 BC in the aftermath of the Pyrrhic War, in which the Graeco-Italian Poseidonians sided with king Pyrrhus of Epirus against the Roman Republic. During the Carthaginian invasion of Italy by Hannibal, the city remained faithful to Rome and afterward, was granted special favours such as the minting of its own coinage. The city continued to prosper during the Roman imperial period and became a bishopric as the Roman Catholic Diocese of Pesto around 400 AD. It started to go into decline between the fourth and seventh centuries AD, and was abandoned during the Middle Ages. The bishopric was suppressed in 1100. Like Naples and most of the surrounding region, the inhabitants presumably spoke a Greek dialect throughout its history. The decline and desertion were probably due to changes in local land drainage patterns, leading to swampy malarial conditions. Raids by "Saracen" pirates and slavers also may have been a deciding factor. The remaining population seems to have moved to the more easily defended cliff-top settlement at Agropoli (i.e. "acropolis" or "citadel" in Greek), a few kilometres away, although this settlement became a base for Muslim raiders for a period. The Paestum site became overgrown and largely forgotten, although some