Sestri Levante has its origins as an ancient maritime and merchant center. Originally a small island with a promontory, it was later connected to the mainland. In Roman times, it was known as Segesta Tigullorum (or Tigulliorum) or simply Segesta. It was mentioned in the year 909 in a certificate of a man named Berengario, in which part of its territory was ceded to the basilica di San Giovanni di Pavia; after it was invaded by the Barbarians. During the Middle Ages, Sestri Levante began to expand, probably giving the fortress appearance that is due to the terrain.
In 1133, the noble family of Lavagna, the Fieschi, attacked Tigullio, the gulf in which Sestri Levante is located, however, they were fought off by the powerful Republic of Genoa, and therefore, Sestri Levante became a part of the republic, for military protection. In the year 1145, the abbey of San Colombano was acquired by the Genoese, and was transformed later into a castle.
In 1170, Sestri Levante was attacked by a naval flotilla from Pisa, but was able to withstand the attack.
Sestri Levante is mentioned by Dante Alighieri (as "Siestri") in Canto 19 of The Divine Comedy
