Until the end of the sixteenth century the square was a very heterogeneous place, in part still characterized by medieval aspects (the castle, the water banks of Doragrossa in Via Garibaldi and the moats outside the walls, the Porta Fibellona, etc.). However, in 1587 a ducal license reveals the existence of a first urban plan that provides the renovation of the Piazza Castello and the buildings that overlooked the square, the southern expansion of the city with the demolition of the walls, the realization of Porta Nuova.
The site locates in the Map of 1605 of Monsa the existing elements: F: the Ducal Palace, C: the Old Castle, T: the Fibellona Gate, N: Dora Grande (Via Garibaldi), H: the Senate (Piazza IV Marzo), P: the new road (via Roma), O: the arcades