The Castle of Saint-Mer was built in 1397-1425 on the hill of Cité in the centre of Lausanne on the site of the old monastery of Saint Marius, which had been moved to another location. The construction of a powerful fortress began on the initiative of Bishop Guillaume de Menton. The future episcopal residence was completed under the next bishop, Guillaume de Challot.
The castle is named after Marius d'Avanche, a late 6th century bishop, also called Saint-Mer or Saint Marius. Bishop Marius transferred the bishopric from Avanche to Lausanne. In 10th century documents we can read that in 581 the pressure of Germanic tribes from the north increased, so the highest church hierarchs did not feel safe and had to move to a building on the hill of Cité in Lausanne.
The castle of Saint-Mer, designed for defence and housing, was built, like many other castles of the era, such as Wuffelens-le-Chateau or Blonet, in the shape of a large cube. The 25X23 metre square fortress rose 25 metres on the south side. The walls were 2.8 metres thick. The upper part of the castle was built of bricks. This indicates that the builders of the castle were invited from Lombardy. With its appearance, the powerful fortress of Saint-Mer reminds of the palaces of the French royal domain (Louvre, Vincennes). Originally, this structure was separated from the rest of the city by one or more enclosures and a dry moat to the west.
In 1536, Lausanne became another prey to the army of Berne, the Château Saint-Maire was turned into an administrative building and arms depot. In 1803 the government of the canton settled here. The fortress was hastily put in order: the tower that was in the way of laying new streets was demolished, the entrance gate was removed, and the garden adjacent to the castle was levelled to the ground. The castle took its present form. It still houses the offices of the government of the Canton of Vaud.
