Greek settlers from Sybaris founded Poseidonia on the fertile Sele plain around 600 BCE. The colony controlled agricultural land and maritime routes and honored deities through monumental sanctuaries. Its earliest great Doric temple, traditionally called the Basilica but now identified as a temple of Hera, rose in the sixth century BCE. A second Hera temple and the Temple of Athena followed. Local people the Greeks called Lucanians took control in the later fifth century, adapting rather than erasing the city. Rome established the colony of Paestum there in 273 BCE.

Roman construction inserted a forum, comitium, amphitheater, baths, houses, roads, and drainage into the older Greek plan. Temples remained prominent even as political and religious life changed. The city's painted tombs, especially the Tomb of the Diver, provide rare evidence for elite funerary imagery in Greek southern Italy. Malaria, changing waterways, economic shifts, and coastal insecurity contributed to gradual abandonment in the early medieval period. Later settlement moved toward higher ground. Marsh and vegetation isolated Paestum, but that decline spared its temples from the intensive stone reuse that destroyed many ancient cities.

Velia began as Elea, founded about 540 BCE by Greek-speaking Phocaean refugees after Persian expansion in Asia Minor. It developed on a coastal promontory and became associated with philosophers Parmenides and Zeno, whose Eleatic school explored being, change, reason, and perception. Rome later called the city Velia. Walls, terraces, streets, baths, houses, and sanctuaries reveal a community shaped by difficult terrain. The so-called Porta Rosa, a masonry arch connecting urban levels, is a striking surviving feature, though older claims about its uniqueness or precise engineering role require caution.

Antiquarian attention and systematic excavation exposed both sites from the eighteenth century onward. At Paestum, the standing temples helped shape European appreciation of Greek Doric architecture and influenced neoclassicism. Excavators uncovered urban blocks, sanctuaries, tombs, and portable finds now protected in the museum. At Velia, investigation continues across the acropolis and lower town. Conservation consolidates stone and roofs, manages vegetation and drainage, and sometimes re-erects architectural elements through anastylosis. Visitors therefore see ancient fabric combined with documented stabilization, not complete reconstructions of inhabited classical cities.

The Italian Ministry of Culture manages Paestum and Velia together through a dedicated archaeological park, with coordinated ticketing, museums, research, and conservation. UNESCO inscribed them in 1998 within the Cilento and Vallo di Diano property, which also includes the cultural landscape and Certosa di Padula. Paestum's three temples remain unusually complete standing structures, while most civic buildings survive as foundations; Velia is more fragmentary but preserves its topography and philosophical associations. The joined park presents two different Greek colonial histories transformed by Lucanian, Roman, Christian, environmental, archaeological, and modern heritage processes.