Many Cadomian and Early Paleozoic basement units in the Alps are considered to be derived from the East Armorican segment of the Gondwana margin. A common assumption is that this East Armorican crustal segment was shifted into the hinterland of West Armorica via a Variscan dextral shear zone. However, the tectonic separation of West and East Armorica could have started earlier during a Late Devonian rifting event. The respective rift zone is supposed to be hidden under the northern nappes of the Alpine–Carpathian chain. This newly proposed sub-Alpine “Cetic rift” was presumably connected with the Upper Devonian Brevenne rift, which is documented in the northern French Massif Central, the southern Vosges and the southern Black Forest. The combined Brevenne–Cetic rift zone may thus represent a major trans-European structure. It is tentatively interpreted as an ephemeral back-arc rift that opened due to southward subduction activities on the northern side of West Armorica.