The Trench of the Blood was used for blood-baptism and the sacrifice of the bull. It was made in the Porta Laurentina, in the extreme east corner of the Campus of the Magna Mater. Two treads between brick piers lead to a floor of opus spicatum. From there a narrow staircase with travertine treads leads to a small underground room, with a vault in the back. Holes indicate that this room was covered with a grate. In each of the side walls is a rectangular niche, in the back wall a semicircular one.
Plan of the east part of the temple-complex of the Magna Mater.
From Vermaseren 1977, fig. 24.