From: Ralph Merrifield, "London: City of the Romans", 1983, p.185:
Head of Mithras in Italian marble, attributed to about 180-200; found in two pieces carefully bured in the Walbrook Mithraeum (see p.211-2). Height 14 1/2 in (37 cm). Museum of London." p.184: "almost certainly fitted to the principal cult image, a group representing Mithras slaying the bull, which would have stood in the sanctuary within the western apse. Professor Toynbee has commented that its general style, and particularly the way in which the hair is worked, point to a date between 180 and 200. There is also a figure of a Genius, which she suggests could have come from the hand of an Italian carver of the mid-second century. There is a very classical head of Minerva, which she assigns to 'the hellenizing phase of Roman artistic taste during the central decades of the second century.' There is a river-god, which she dates on grounds of technique and style to the second quarter or middle of the second century. Finally there is a very fine head of the Egyptian god Serapis, which should not be earlier than the last quarter of the second century. We have, therefore, a group of imported marble sculptures ranging in date, in Professor Toynbee's expert opinion, from at least the middle of the second century almost to its end.
Marble head of Mithras in Phrygian cap (Illustrated London News 1954,542).