These messengers customarily carried their dispatches in sturdy leather pouches called Valigie, which gave us the modern French word ‘valise’, meaning suitcase.
A large number were unearthed during preliminary construction work, which led directly to the discovery of the temple.
The site was secured pending completion of the terminal, and kept under wraps until now.
The remains were discovered in the path of the 11 mile underground baggage conveyor complex, which had to be re-routed by several hundred yards as a result.
BAA have denied that the resulting kink in the path of the conveyor belts – as well as an unusual zig-zag section to skirt a series of massive marble columns - contributed to the recent baggage problems at the new Terminal.
During the planned excavations a number of flights are expected to be
re-routed to a sixth, temporary Terminal, on the far perimeter of the airport.
When asked about the impact on planning for a possible third runway, Professor Buffon said:
"Mithraic Temples are seldom found in isolation.
"We would not be surprised if there was a whole town under there.
"We're also expecting to find a whole lot more structures under Heathrow - so don't hold your breath for a third runway anytime soon!"
Professor Avril Buffon is an archeology fellow of the Institute of Classical Archaeology at the University of Nantes.
She has been working in the archeology field for over 15 years, and recently came to the public's attention with her discovery of a roman villa under Highbury Football Stadium.
Her current work at Heathrow Airport Terminal began in early 2007.