thumb|right|Example of opus mixtum in the substruction of Brest Castle, FranceOpus mixtum (Latin: "mixed work"), or opus vagecum and opus compositum, was an ancient Roman construction technique. It can consist in a mix of opus reticulatum and at the angles and the sides of opus latericium. It can also consist of opus vittatum and opus testaceum. Opus mixtum was also used from the 4th to 6th centuries AD.[1]