[2] The palace was initially designed to be a square “palazzo-fortezza,” or palace-fortress, featuring four prominent diamond-shaped bastions, a large internal courtyard surrounded by a loggia of 24 sandstone columns, and a central well.

While some historians credit Donato Bramante, others suggest Francesco da Sangallo as the designer, and current consensus tends to favor the latter.

[3] The architectural style of the palace demonstrates features typical of military fortresses from the late 15th century, adapted to defend against contemporary artillery advances.

Following the deaths of Cesare and Rizzardo Alidosi, work on the palace ceased, leaving the southwest and northwest bastions unfinished.

The palace subsequently fell into decline after Castel del Rio became part of the Papal States in 1683 under Pope Urban VIII.