Cult of Mithras

The cult of Mithras was a Roman "mystery religion", centring around the god Mithras, which originated from Mithras of Indo-European origin. Mithras was associated with contracts, friendship and cosmic order. 

Mystery religions, or mystery cults, sometimes shortened simply to mysteries, were religious schools participation in which was reserved to initiates. A famous cult of pre-Greek origins was the Eleusinian Mysteries.

Mithraism became popular in Italy, Britain and North Africa and survived prior to the advent of Christianity. 

Rituals took place in underground temples called mithraea. There are a number in the city of Rome. There are remains of one near Hexham in Northumberland, England, and also one in London.