Sasayama site, Archaeological site in Tokamachi, Japan.

Sasayama is an archaeological site in Tokamachi, in Niigata Prefecture, where excavations have uncovered settlement remains, stone tools, and pottery from several prehistoric periods. The site is divided into multiple digging areas, each revealing layers that correspond to different phases of occupation.

The area around Tokamachi has been settled since prehistoric times, and excavations at Sasayama revealed that the site was occupied across several consecutive periods without long interruption. The sequence of layers shows that different groups came and went, each leaving behind a distinct set of objects and traces.

The site gives its name to the Sasayama Jōmon Market, held once a year since 2000 by the Nakajō district promotion association to mark the national treasure designation. Local neighbourhood associations and groups run stalls on a Jōmon theme, schoolchildren perform, and guests have included the actor Shunsuke Kariya; recent editions draw over 2,000 visitors.

Tokamachi is reachable by Shinkansen, but getting to the site itself requires local transport or a car for the final stretch. As this is an active research location, it is worth checking access conditions before heading out.

The 57 deep bowls excavated here, including 14 flame-style vessels, were designated a National Treasure in 1999 and are held at the Tokamachi City Museum. They are the only Jomon pottery so designated and Niigata Prefecture's only National Treasure. Since 2000 the Nakajo district holds the annual Sasayama Jomon Market, with stalls and school performances.