Iesi (Italian: Jesi) is a town and comune of the Province of Ancona in the Marche, Italy. It is an important industrial and artistic center in the floodplain on the left (north) bank of the Esino river 17 kilometres (11 mi) before its mouth on the Adriatic Sea.
Iesi was one of the last towns of the Umbri when, in the 4th century BC, the Senones Gauls invaded the area and ousted them. They turned it into a stronghold against the Piceni. In 283 BC the Senones were defeated by the Romans. Iesi in 247 BC became a colonia civium romanorum with the name of Aesis.
- The Cathedral (Duomo), built in the 13th-15th centuries.
- Palazzo della Signoria, built in 1486-1498 by Francesco di Giorgio Martini.
- Palazzo Balleani, an example of local Baroque architecture, built from 1720.
- The convent of San Floriano (18th century).
- The 14th century walls.
- Church of San Marco, just outside the historical centre.
- Palazzo Ricci, finished in 1547.
- Teatro Pergolesi, built in 1790.
- Palazzo Pianetti, one of the most outstanding examples of Italian Roccoco art.
- The church of Santa Maria delle Grazie (15th century).
- The 13th century church of San Nicolò.