By 1246, Ferdinand III had already taken Cordoba in a rapid conquest that sent shockwaves through the Muslim world. After the fall of Jaen that year, only two major cities in Iberia remained outside Christian suzerainty: Seville and Granada. Of the two, Seville was the greater prize -- a wealthy river port, the seat of Almohad power in Al-Andalus, and a city whose walls had held for centuries. Ferdinand massed his armies to the north and east during the summer of 1247, methodically cutting the city's overland supply routes and tightening the noose before committing to a full siege.

The campaign's decisive stroke came from the river. Ramon de Bonifaz sailed thirteen galleys and a flotilla of smaller vessels up the Guadalquivir, scattering some forty Muslim boats that tried to block his passage. The defenders had stretched a great chain between the Torre del Oro and an anchor point on the opposite bank -- a boom designed to prevent any fleet from reaching the city's wharves. Bonifaz broke through it, severing Seville's connection to Triana on the far bank and cutting the pontoon bridge that linked the two. Though Bonifaz never held an official title, he is remembered as the first admiral of Castile, the man who proved that landlocked Castile-Leon could fight and win on water.

With the river blockaded and overland routes sealed, famine took hold inside the walls. St. Albertus Magnus later wrote that the Moorish defenders deployed artillery loaded with rocks, though whether these constituted true firearms remains a matter of scholarly debate. What is certain is that hunger, not bombardment, broke the city's resistance. On 23 November 1248, Seville capitulated. The terms stipulated that Castilian troops would enter the Alcazar within a month. Ferdinand made his triumphant entry on 22 December 1248. Muslim chronicles record that some 300,000 inhabitants left the city, though the historian O'Callaghan considers this figure exaggerated. Whatever the true number, the departure was massive -- a population emptying from a city that had been Muslim for over five centuries.

Ferdinand's conquest transformed Seville. The grand Almohad mosque became a Christian cathedral -- the same site where, a century and a half later, builders would erect the largest Gothic cathedral in the world. The Alcazar became a royal palace. The Torre del Oro, which had anchored the chain Bonifaz shattered, stood as a watchtower on the Guadalquivir for centuries to come. Ferdinand III himself was buried in the royal chapel of the cathedral he had consecrated, and was canonized in 1671. The siege of Seville marked the effective end of the Early Reconquista. After 1248, the frontier between Christian and Muslim Spain would shift only slowly, and Granada would not fall until 1492 -- but the strategic balance had already tipped irreversibly on the banks of the Guadalquivir.