Roman, which are far less well preserved. Paestum is far from any sources of good marble. Unsurprisingly, the three main temples had few stone reliefs, perhaps using painting instead. Painted terracotta was used for some detailed parts of the structure. The large pieces of terracotta that have survived are in the museum. The whole ancient city of Paestum covered an area of approximately 120 hectares. Only the 25 hectares that contain the three main temples and the other main buildings have been excavated. The other 95 hectares remain on private land and have not been studied. The ancient city was surrounded by defensive walls, which are largely intact. The walls are approximately long in its polygonal perimeter, typically high, and thick. Corresponding with the cardinal points, there were four main openings in the wall: Porta Sirena (east to the hills); Porta Giustizia (south, now to the modern village Paestum); Porta Marina (west to the sea); and Porta Aurea (north), which was later destroyed. Positioned along the wall were 24 square or round towers. There may have been as many as 28, but some of them (and Porta Aurea) were destroyed during the construction of a highway during the 18th century that effectively cut the ancient site in two. The central area is completely clear of modern buildings and always has been largely so, since the Middle Ages. Although much stone has been stripped from the site, large numbers of buildings remain detectable by their footings or the lower parts of their walls, and the main roads remain paved. A low-built heroon or shrine memorial to an unknown local hero survived intact; the contents are in the museum. Numerous tombs have been excavated outside the walls. The three Greek Temples The first Temple of Hera, built around 550 BC by the Greek colonists, is the oldest surviving temple in Paestum and the one farthest south. 18th-century archaeologists named it "the Basilica" because some mistakenly believed it to be a Roman building. (The original Roman basilica was essentially a civic form of building, before the basilica plan was adopted by the Early Christians for churches.) Inscriptions and terracotta statuettes revealed that the goddess worshiped here was Hera. Later, an altar was unearthed in front of the temple, in the open-air site usual for a Greek altar. The faithful could attend rites and sacrifices without entering the cella or inner sanctuary. The columns