The building of the castello

The small suburb was literally razed to the ground and the grandiose building project got under way. Twenty years after its destruction, the Church of San Giuliano was rebuilt not far away, where it's still stands today. Bartolino da Novara, already famous as a designer and builder of churches and fortifications, designed the Castello di San Michele, based on the existing, defensive hub of the Rocca del Leone, which he himself had probably already designed.
To get an idea of Bartolino da Novara's design for the Castello di San Michele, take a look at the Castello di San Giorgio a Mantua (although somewhat smaller in size) also designed by Bartolino ten years later for Francesco Gonzaga. The scheme for the project was to add another three towers (named Santa Caterina, San Paolo and Marchesana), of equal size and height, three floors high, laid out to form a four-sided castle to the first tower-fortress by that time commonly known as the Torre dei Leoni, Between one tower and another lay the two floors of the curtain wall, which with its large open courtyard in its interior made it a proper fortress, tall and well-constructed and with an appearance that must have seemed impregnable for that period.
Beneath the stringcourse of the raised ground floor, most of which is spiral shaped stone, the walls taper out and down and the ends are decorated with insignia of the house of Este. As with the smaller fortress, the battlements of the second floor of the curtain wall and those of the third floor of the towers were defended by crenellations projecting on corbels in line with the traditional formulas of military architecture of the period. The basements were built with low barrel vault ceilings that linked the underground rooms of the towers. It is on this massive and mighty structure, more of a foundation element than one of elevation, that the large mass of the castle building rests. The ground floor, raised above the courtyard, consisted of a series of rooms with cross vault ceilings. For the most part, the first floor consisted of wide galleries that linked the towers, which also had cross vault ceilings. The battlements on the second floor were probably covered with roofs made of wood and tiles. To get between the floors there were spiral staircases which ran within the thick external walls. In the basements and on the first floor of the avant-corps and the gatehouses, the openings were embrasures. In the rest of the castle light for the large rooms of the ground and first floors came through small windows. The entire fortress was surrounded by a broad moat; the moat around the Torre dei Leoni, two sides of which were covered by the new building, still existed. The entrances were defended by avant-corps flanking the towers: from these a drawbridge reached across to gatehouses, small auxiliary towers built in the moat; these were then connected to the outside bank of the moat by other bridges.
For the Este family's safety, their residence in the main town square was connected to the Castello di San Michele by means of a bridge from its first floor which, raised above ground level, crossed the space between the two buildings, then crossed the moat and led straight into the fortress courtyard.