Arausio was the name for Orange, in southern France, and the Legio II Augusta was particularly associated with the town. It was based in Britain after the arrival of the Romans, with the main base at Caerleon. From there it provided administrative staff for the Roman governor in London. A reasonably successful military career may have taken the young Ulpius Silvanus
from the olive groves of Provence to the mud of the South East of England.
After his retirement, he may have decided to use what money he had to create a Mithraeum, of which he would, we may assume, have been the leader, the Pater. He may have commissioned the relief that bears his name – but in Orange, probably, certainly not in London. The rest of the sculpture for the temple he might have been picked up second-hand, as it were, either in Italy or perhaps in some merchant's shop in London, imported by other people over the years.
The whole process must have been quite drawn out: the temple was built several decades after the relief was carved. And it is possible that Silvanus, who presumably retired in his forties sometime around 200 CE, was already dead by the time the site for the temple became available.
—Hugh Bowden (2018) When things don't fit: Looking at the London Mithraeum
The image of Mithras killing the bull, found near Walbrook, is surrounded by a Zoadiac circle.
Ulpius Silvanus / factis Arausione / emeritus leg(ionis) II aug(ustae) / votum solvit.
Ulpius Silvanus, veteran of the Legio II Augusta, recruited in Arausio, has fulfilled his vow.