In 1050 massive towers were added to the ends of the groin-vaulted transepts. This is the north tower of the transept. Its name comes from the tomb of Hildegard, the third wife of Charlemagne, buried beneath the tower. Restored in 1928.

The church, built at the site of the tomb of St Martin, Bishop of Tours, became the most famous pilgrimage sanctuary in France. Venerated during his lifetime, Martin was acclaimed a saint at his death in 397, his remains attracting thousands of pilgrims annually for over a millennium. Tension between the bourgeoisie of Tours and the canons erupted in 1122 and the church was set ablaze. Makeshift repairs accelerated deterioration until, by 1160, the building was in urgent need of restoration. This programme initiated the third phase of building. A miniature by Jean Fouquet depicts the Gothic church in 1450. The aisles rose from heights of ca. 9 m and 21 m to the 35.5 m-high nave, and three sets of windows lit the interior. The monumental choir buttresses spanned both ambulatories. The last picture of St Martin, a wash by Pinguet done in 1798, shows the nave in ruins. The so-called Tour de Charlemagne (Tower of Charlemagne) and the Tour de l'Horloge (Clock Tower) are the only remnants of the original building.