From March 1625 the first signs of hostility began, which in a few months resulted in a real war between the Republic and the Duchy of Savoy of Charles Emmanuel I, supported by Kingdom of France of Louis XIII.

During his dogate, the fifty-second in biennial succession and the ninety-seventh in republican history, for obvious reasons he had to deal mainly with the defense of Genoa and the Ligurian territory following the path initially started by his predecessor.

[1] In addition to defending the borders, Doge Lomellini had to face the numerous internal unrest of those territories and populations, with drastic repressions, which, taking advantage of the Savoy-Genoese conflict, expressed their dissensions over economic and social issues, including what became known as the "conspiracy of the De Marini".

A ceremony which, given the recent Genoese successes, consequently enhanced the figure of the crowned doge Giacomo Lomellini among civil, religious, poetic and people's prayers who now saw him as the new "savior of the homeland".

On December 7, 1626 the doge himself laid the foundation stone and in the following years there were numerous donations from individuals, corporations, and the arts, to which were added the new taxes specifically designed to support the expense, paid for the more from the middle and less wealthy classes.