The necropolises in the districts of Costa di Mandorle, Porco Spino, Birrigiolo and Strazzo prove that the first human settlements in the Riesi area date back to the Copper Age. Due to the various dominations, the name of the small town changed in the course of the centuries from Reiz to Rahalmet for the Arabs, from Ries to Riesum for the Normans and the Angevines, to Altarriva, and finally to Riesi.
From the sparse information on Riesi prior to the 12th Century, we can gather the presence of the homestead during the Arab domination and the feuds, partially uncultivated, of the Norman and Angevin periods. In fact, the name Riesi indicates the constant abandonment of the land. In the 16th Century, King Ferdinand II of Aragon granted to Giovanni Rojs de Calcina the "mero e misto imperio" and the licence to populate the land of Riesi and Cipolla. Nevertheless, until 1647, the Riesi barony had no resident population, but only temporary peasants busy in the fields. Piero Altarriva decided to appoint as administrator of the barony Pietro Gilò, who was the actual founder of modern Riesi.
From an economy based on feudalism, the barony moved, in the 18th Century, to an economy mainly based on the extraction of sulphur from the mines not far from town.