The cathedral exists because the statue did first. A twelfth-century carving of the Virgin Mary called Notre-Dame de la Treille had lived for more than six hundred years in the Collegiate Church of Saint-Pierre, in the heart of Lille. The Austrian siege of 1792 damaged the church; the French Revolution finished it. The statue was bought by a sexton named Alain Gambier, who kept it in the Church of St Catherine from 1797 to 1802, and then it largely vanished from public devotion. It was a parish priest, Charles Bernard, who pulled it back into view in the 1840s — instituting a month of Mary, organising a jubilee, and building the political case for a new church large enough to house the cult. The foundation stone was laid on 1 July 1854, the feast of Our Lady of the Treille, by the Archbishop of Cambrai. Ten bishops and the mayor stood watching. Crowds filled the streets.

The 1854 international competition asked for a church "in the Gothic style of the first half of the 13th century." Forty-one entries arrived. The first two prizes both went to English architects — and the moment the names were announced, the project hit a wall. To Lille's Catholic establishment, handing the Virgin's church to Anglicans was unthinkable. The competition was effectively voided. The work went instead to Charles Leroy, a Lille architect whose project drew on the foreign designs without crediting them. Then the money ran out, and ran out again, and ran out for the better part of a century. Generations of architects came and went. The nave inched upward in stages between 1856 and 1975, the choir rising decades before the transepts, the transepts decades before anything thought about the front. By the time Lille got around to its cathedral's facade, the original Gothic Revival movement had been dead for a hundred years.

The church was always meant to be more than a church. In 1852 the Lille deputy Charles Kolb-Bernard published a public report arguing that Lille — a booming industrial city of immigrants from Flemish Belgium, an island of working-class poverty inside the much larger Diocese of Cambrai — needed its own bishop. By 1896, an official report found that twenty-five percent of Lille's residents were not French citizens, and ninety-eight percent of those were Belgian, mainly Flemish-speaking. Kolb-Bernard, an anti-Republican Legitimist with views that today would read as paternalistic at best, framed the new bishopric as a tool for what he called the moralisation of the working class. Whatever one makes of his motives, the new diocese was created, and the half-built church on the old castle mound was designated its cathedral from the start. Land had been bought in 1853 for 223,000 francs — an enormous sum, in the heart of Old Lille.

When Pierre-Louis Carlier and Peter Rice finally got to the facade in the 1990s, they refused to fake more nineteenth-century Gothic. Instead they cut white marble into translucent panels and held them inside a steel grid that follows the lines the original architects had drawn but never built. From the square outside, the wall reads as warm cream limestone. From inside, with the sun behind it, the whole front glows. The great rose window — designed by the Hungarian-French artist Ladislas Kijno and the stained-glass master Gérard Lardeur — sits in the centre of that glowing wall like a colour test. The cathedral was finally consecrated in 1999. A hundred and forty-five years from foundation stone to last panel. Old Lille kept building it, and waiting, and building it again, until the technology arrived that could finish what faith had started.