It had a castle which was enlarged by the Angevines and, during the reign of Alfonso V of Aragon, housed his mistress Lucrezia d'Alagno.

Caiazzo was the seat of anti-royal rebellions at the times of the Neapolitan Republic, and also housed several Carbonari.

Despite this, Caiazzo was one of the few towns in the kingdom whose population sided against Garibaldi's expedition which annexed southern Italy to Piedmont.

During World War II, retreating German troops massacred 22 civilians here.

Caiazzo has remains of Cyclopean or polygonal masonry walls, and under the Piazza del Mercato is a large Roman cistern, which for centuries continued to provide a good water supply.