Alberobello was first mentioned in the early 16th century when the first 40 families were granted land to farm in the area. The abundance of calcareous sedimentary material in the area lead to the building of houses with dry stone without the use of mortar. These houses were the first trulli which contributed to the expansion of the settlement. Building the houses of dry stone was a requirement of Count Giangirolamo II as in this way it was avoidable to pay taxes on them. The inhabitants of Alberobello were feudal vassals of the Acquaviva of Aragon until May 27, 1797, when King Ferdinand IV of Bourbon received Alberobello and issued a decree that elevated the small village to a royal city, freeing them from feudal serfdom.