Reputed to be Thailand's oldest city (it's thought to date from 150 BC), Nakhon Pathom was once the center of the Dvaravati kingdom, a 6th- to 11th-century affiliation of Mon city-states. It marks the region's first center of Buddhist learning, established about a millennium ago. Today, there would be little reason to visit if it weren't for the Buddhist monument Phra Pathom Chedi.