The roof of the 13th-century Palais Synodal, alongside Sens's cathedral, is notable for its yellow, green, and red diamond-tile motif—incongruously added in the mid-19th century by monument restorer Viollet-le-Duc. Six grand windows and the vaulted Synodal Hall are outstanding architectural features; the building now functions as an exhibition space. Annexed to the Palais is an ensemble of Renaissance buildings with a courtyard offering a fine view of the cathedral's Flamboyant Gothic south transept, constructed by master stonemason Martin Chambiges at the start of the 16th century (rose windows were his specialty, as you can appreciate here). Inside is a museum with archaeological finds from the Gallo-Roman period. The cathedral treasury, now on the museum's first floor, is one of the richest in France, comparable to that of Conques. It contains a collection of miters, ivories, the shrouds of St. Sivard and St. Loup, and sumptuous reliquaries. But the star of the collection is Thomas à Becket's restored brown-and-silver-edged linen robe. His chasuble, stole, and sandals are too fragile to display.