Carlo Emanuele I created a diplomatic network and, in order to include the Duchy of Savoy in his European strategy, Cristina of Bourbon, sister of Louis XIII, daughter of Henri IV King of France and of Maria de’ Medici, was given in marriage to the young Vittorio Amedeo1. The Franco-Savoy alliance was thereby strengthened, orienting the Duchy’s policy towards a more explicitly anti-Spanish line. The wedding was celebrated in the chapel of the Louvre on 10 February 1619, the birthday of thirteen-year-old Cristina. Cristina arrived in Turin in spring 1620: she was a young lady whose future was bent towards international politics and the need to seek a further link between the two neighbouring powers. For the occasion of Cristina’s arrival in Turin, the city designed by Ascanio Vitozzi and by Carlo di Castellamonte came to life: the palaces became a backdrop animated by allegorical statues, the gate of the «new city» was a monumental entrance to the southern extension, inaugurated for that occasion; at the most ancient core of the Roman-founded grid system, the first seventeenth-century enlargement, to the south, was hinged around the building fabric which had been moulded mainly during the lengthy Middle Ages. Today’s Piazza San Carlo, then known as the «great Castellamonte theatre», was designed as a uniform system and was the most important space in the expansion; it also represented the fulcrum of a new urban entity, reflecting the authority and continuity of the Savoy dynasty. In the seventeenth-century design, twin churches, San Carlo and Santa Cristina, were built like two stage wings to frame the entrance of the southern section of Contrada Nuova (now Via Roma). The convent annexed to Santa Cristina, now demolished, was home to the Discalced Carmelite nuns, summoned to Turin by Cristina who chose their monastery for her spiritual retreats. Carlo di Castellamonte, superintendent of all the ducal sites, was the architect of the urban project which was based on Vitozzi’s plan.