A 'seminary for foreign missions' had been set up on rue du Bac in 1637 by Monseigneur Duval, with an accord from pope Urban VIII, during the Counter Reformation. The seminary's oratory or chapel was built between 1683 and 1689, with interior decoration by Jacques Stella, Nicolas Poussin and Simon Vouet, and it was this chapel that operated secretly as a parish church for the area during the Revolutionary era when the area's actual parish church of Saint-Sulpice was shut down. In 1801 the chapel was attached to the church of Saint-Thomas-d’Aquin, which became the church for the Faubourg Saint-Germain, and the 'Missions étrangères' parish was officially recognised and split from the parish of Saint-Sulpice in 1802, at which time its curé was abbé Dessaubaz.
40 years later, in 1842, the parish was dedicated to St Francis Xavier. However, the chapel soon became too cramped for the seminarians and parishioners to share and the parishioners began construction on a new church in 1861 under abbé Jean-Louis Roquette (curé of the church from 1848 to 1889), headed by Adrien Lusson then Joseph Uchard and paid for by the Ville de Paris. The chosen site was in the corner of boulevard des Invalides and a planned boulevard right across the district towards rue des Saints-Pères that would meet the Seine level with pont du Carrousel. According to the principals of Haussmann's renovation of Paris, the new church would then form the end to this planned boulevard, explaining why its siting seems odd today, shifted over the boulevard and the hôtel des Invalides. Lusson began the works, but they were interrupted in 1863 and resumed under Uchard after Lusson's death. Work on the exterior was completed on 15 July 1874 and inaugurated at Easter 1875, at which point the interior decor was still incomplete. It was finally consecrated on 23 May 1894, the eve of Corpus Christi, in a ceremony presided over by François-Marie-Benjamin Richard, archbishop of Paris.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.