This mithraeum was excavated by the Irish painter Robert Fagan between 1794 and 1802. Today it cannot be seen. It must be somewhere between the Palazzo Imperiale and the ancient mouth of the Tiber (Tor Boacciana). In the shrine a marble sculptural group was found of Mithras killing the bull (now in the Vatican Museums). He is called "undiscoverable deity" in an inscription on the basis:
SIG(num) INDEPREHENSIVILIS DEI C(aius) VALERIVS HERACLES SACERDOS S(ua) P(ecunia) P(osuit)
L(ucius) SEXTIVS KARVS ET
The second line was added later and should be understood as being in front of C. Valerius.
Furthermore a curious marble statue was found (now in the Vatican Library). It was painted red. It is a representation of time: a naked body in the coils of a snake and with the head of a lion. In its hands are two keys and a sceptre. It has four wings, symbols of the seasons. It was dedicated by a "father" and two priests, witness an inscription from 13 August 190 AD:
VS HERACLES PAT(er)
ET C(aii) VALERII
VITALIS ET NICO
TES S(ua) P(e)C(unia) P(o)S(ue)R(unt)
D(e)D(icatum) IDI(bus) AVG(ustis) IMP(eratore)
A similar, gilded figure is seen on a marble relief from the shrine (now in the Vatican Museums). Also from the shrine comes the following inscription:
C(aius) VALERIVS HERACLES PAT[e]R E[t] A[ntis]
TES DEI IV[b]ENIS INCONRVPTI S[ol]IS INVICTI MITHRA[e]
[c]RYPTAM PALATI CONCESSA[m] SIBI A M(arco) AVRELIO
Apparently the shrine was installed in an (underground?) crypta of an Imperial palace, after approval by M. Aurelius (the Emperor Commodus, or an Imperial freedman). Commodus had been initiated in the mysteries of Mithras: Sacra Mithriaca homicidio vero polluit, cum illic aliquid ad speciem timoris vel dici vel fingi soleat ("He desecrated the rites of Mithras with actual murder, although it was customary in them merely to say or pretend something that would produce an impression of terror"; SHA, Commodus IX,6).
The group of Mithras killing the bull. SO II, Tav. XXXIV, 2.
The statue and relief of time. SO II, Tav. XXXVI, 1-2.