Bucrania on a building in Poitiers (now a private health insurance agency).
The answer is to be found in the way European culture looked back on Roman times as the good old days. Roman motifs and symbolic references to Rome appear everywhere throughout the post Roman period.
La Chancellerie in Loches, with both ox skulls and ox heads. The bucrania on this building are not as fine as the ones in Poitiers that I photographed.
Ox head, Loches.