Gisacum was a Gallo-Roman religious sanctuary near the settlement of Mediolanum Aulercorum (Évreux) in the territory of the Eburovices[1] in northern Gaul (now Normandy). The site lies within the territory of the commune of Le Vieil-Évreux ("Old Évreux").
In the 1st century AD a vast sanctuary was laid out, about 6 km southeast of Mediolanum Aulercorum, on an all-but-unique plan: monumental public structures isolated at the center were surrounded by a vast empty space, with the urban habitations around a hexagonal periphery, 5.6 km in circumference, enclosing an area of some 2.5 km².
Gisacum has been excavated with increasing care since the early 19th century. The recent campaigns began in 1996.