In the first half of the Seventeenth century, some of the most important and prolific military engineers at the service of Spain focused their attention on the northern Italian peninsula. In particular, interests laid on the border between the State of Milan and the Duchy of Savoy. In few decades, actions of fortification reinforcement of the cities located in the border were undertaken, along with the aggression and the conquest of some Piedmont’s obsolete fortresses subsequently reinforced in the walls and the defence aimed at the prevention of a France-Savoy counterattack, after the unsuccessful sieges of Turin and Casale Monferrato (1640). Especially starting from the 1630s, Francesco Prestino stood out as " ingegnere maggiore dell’Esercito di sua maestà nostro signore nel Stato di Milano”. In 1633, he was commissioned by Philip IV to draw an atlas of cities of the State of Milan, not yet identified. Teacher of Gaspare Beretta, who will replace him after his death, he was committed to the defence of the cities of the State of Milan during the war that broke out after the death of Vittorio Amedeo I of Savoy and the occupation of Piedmont by the Marquis of Leganés. Active in the newly Spanish fortress of Vercelli, he dealt with the strengthening and the maintenance of the walls signing, in the first half of the 1640s, a series of reports on the conditions of the fortresses of the State of Milan. The documents must be linked to an atlas of drawings preserved in the Biblioteca Nacional de España (already the subject of a contribution in the conference Fortmed 2015) and to a series of drawings dated 1642, preserved in the Biblioteca Ambrosiana of Milan and signed by Giovanni Giacomo Tensini, a military engineer who was also active in Gaspare Beretta’s entourage.