The cathedral (former collegiate church) is one of the hugest church in Haut-Rhin département! In the past, it was a small oratory raised in the 9th century by monks from abbey of Munster. In 1234, pope Gregory IX allowed the construction of a Romanesque collegiate church in order to replace the oratory. But 3 years later, bishop of Basel, Henri de Thoune, established a chapter in Saint-Martin: the church had to be extended!
Building work began in 1263: transept, nave and front were raised. In the middle of the 14th century, they finished with the choir. A little restoration was made in 1559, but in 1572, a fire devastated the bell-tower. In 1720, they destroyed the rood-screen, then 60 years later, the chapter disappeared with the Revolution.
Did you know the two towers flanking the Western portal remained uncompleted? The Southern one was higher than the Northern one; the first one was burnt in 1572, later replaced by a campanile. During centuries, the cathedral houses a 15th century triptych completed by Martin Schongauer, called the "Roses Bush's Virgin". It was stolen in 1792, then found again; now they keep it in Colmar Dominican church.