The construction of the Church of St. Blaise and St. John the Baptist (Dom St. Blasii et Johannis) began during the life of the Duke Henry the Lion. He and his wife Mathilde were buried here before the end of the construction. Their son, Roman Emperor Otto IV is also buried here. The building of the cathedral was rebuilt in the XIV-XV centuries. The eastern part is the oldest. The pure architectural style of the Romanesque period was retained in it. The wooden cross created by master Imervard in the second half of the XII century is one of the main values of the cathedral.
The Gothic tombstone of Henry and Mathilde is also of interest. It depicts the Duke as a young soldier with the model of the cathedral in his hand. The “Lion's portal” is in the northern part of the cathedral. According to legend, Henry's favorite lion scratched the wall stricken by the grief of its owner’s death. The more prosaic explanation is that medieval knights sharpened their swords here before the start of the campaign.