The colony took the name Caianum, then with the transition from Latin to the vernacular, the name became Caiano and later Caianello. Of those ancient origins only historical memories remain, place names, and ruins of Roman tombs dating to the 3rd and 4th century BC.
Caianello was inhabited in medieval times, as evidenced both by a papal bull of 1193 and the Catalogus Baronum of William II (1188). In 1275-1277 Caianello contributed to the fleet of King Charles I of Anjou in the campaign against the Emperor of Constantinople. From 1345 onwards the town belonged to various feudal lords, among whom Francesco Del Balzo, the Abenavoli family (1406), Petrillo de Aurilia, the Transo family, Nicola Anotinio de Montibus (1467), Consalvo de Cordoba (1514), Cesare de Capua (1637), Salvatore del Pezzo (1745).