The Duke of Alba at Saint Gudule's in Brussels

Ingres began this in Rome in 1815, the year Napoleon's empire finally fell and French artists in Italy lost their patrons almost overnight. The commission asked him to show the Duke of Alba — the Spanish general whose 'Council of Blood' terrorised the Netherlands in the 1560s — receiving a papal blessing in the cathedral of Sainte-Gudule in Brussels. It was a strange thing to hand a French painter, and Ingres never finished it; the canvas stayed in his studio for the rest of his long life. Long after, it passed to Edgar Degas, who idolised Ingres and hunted down his work. What survives is a crowded church interior, half-drawn, the kneeling duke barely more than an outline.