The Mithraeum of the Planta Pedis ("footprint") is so-called because the mosaic floor has a mosaic of a single foot-print in it.
A Mithraeum (Reg. In, Is. XVII, 2) constructed in a building from the Hadrian
period ("Mitreo della planta pedis"), situated near Horrea and a Serapeum.
Becatti, Mitrei Ostia, 77ff, fig. 18 and Pls. XV, XVI, 3. See fig. 80.
The part of the house transformed into a Mithraeum has two rows of three
pillars, which divide the sanctuary into three sections. In the middle section runs
a central-aisle between two small benches (H. 0.40 Br. 0.25), constructed against
the pillars. In the right bench, before the middle pillar, is a small rectangular
depression (L. 0.10) and in its base a niche (H. 0;35 Br. 0.42 D. 0.30) in which
bones of fowls have been found. The niche in the opposite bench is deeper (D. 0.60
Br. 0.42). It seems that behind this bench a larger one extends in the left section
(Br. 2.00) of the sanctuary. At the end of the r. bench an entrance (Br. 1.10) had
been made in the side wall, the main entrance, however, was opposite the cult-niche
(Br. 0.80). The niche had three levels: the first (H. 0.55 D. 0.75) is covered
with black-white mosaic (five crosses between two squares); the second level (H. 0.25 D. 0.50) had a marble revetment; the third (H. 0.44 D. 0.70) had a small rectangular brick base.
A base is (H. 0.50--0.60 Br. 0.30) on either side before the niche, probably for statues of the torchbearers (lost). Between them is a marble altar (H. 1.00 Br. 0.34 D. 0.30) in the top of which is a depression.
The floor of the central-aisle has a mosaic decoration, existing of a small black line approximately in the centre of the sanctuary. Near this band there is the representation of a serpent (L. 1.00), whereas near the entrance a foot is visible. The original floor of the Mithraeum, however, had only a simple pavement of cocciopisto and in it on the same place a footmark was imprinted. (Becatti, Pl. XVI, 1).