ON what is now Christmas Day, troops on Hadrian's Wall 1,800 years ago were celebrating the birthday of the god Mithras.
Born on December 25, Mithras was worshipped at sites on at least three locations along the Wall.
Now conservation work is to be carried out on a sculpture of Mithras which was discovered at Housesteads Roman fort in the 19th Century.
The stone relief shows Mithras emerging from the Orphic Egg – the symbol of eternal time.
The god is surrounded by an egg-shaped representation of the signs of the zodiac, representing the cosmos.
This is the earliest representation of the signs of the zodiac to be found in Britain.
It would have been lit from behind to present a powerful image for worshippers entering the semi-underground temple at Chapel Hill at Housesteads.
The sculpture is one of the main exhibits in a collection of Mithraic items from the Wall on show at the Great North Museum in Newcastle.
"It is one of the best collections of Mithraic material in the world," said Andrew Parkin, keeper of archaeology at Tyne Wear Archives and Museums.
Repair and conservation work will now take place on restoration measures carried out on the sculpture in the 1950s, which are deteriorating.
"It will be painstaking work undertaken by our experienced conservation team," said Andrew. He hopes the sculpture will be back on display in February.
The carving is usually on display underneath a relief sculpture which shows a scene of Mithras slaying a bull, which was also found at Housesteads and was a common depiction in Mithraic temples.
"Our Mithras stone is a unique and powerful Roman object that blends several religious traditions," Andrew said. "We still have offerings left at the museum at this time of year. Previously we've had a pot plant, pine cones, money and even a Chocolate Orange."
The stone is part of the Society of Antiquaries of Newcastle upon Tyne's collection.
The cult of Mithras was popular amongst the military and originated around 1400 BC in Persia.
It was confined to male worshippers and involved progression through several grades of worship with different ranks and costumes.
Mithraic temples have been identified in Northumberland at Housesteads, Rudchester and Carrawburgh, where three altars were found along with the remains of cockerels which had probably been sacrificed and statues of the god's helpers.
The complex imagery of the Housesteads sculpture suggests the sophistication of the cult at the fort. The celebration of Christmas became superimposed on earlier religious and ritual practices.
"To some extent there have always been mid-winter festivals at what is the darkest part of the year to mark the turning point when it will begin getting lighter," said Andrew. "In the early days Christianity was competing with a lot of different cults around the world."
Mithras was celebrated as the Lord of Ages and a god of light, who is often shown carrying a torch and bringing light to the world.