The carefully hidden dirt was the first clue and the subsequent collapse confirmed it: as the concrete walls and decaying cell blocks are being dismantled, the Maze is finally giving up some of its secrets.
Workmen demolishing the last traces of the first prison compound, where hundreds of republicans and loyalists were interned or jailed in the Seventies, have found a long forgotten escape tunnel.
The tunnel, which ran for about 60 feet from the Nissen huts of the old Long Kesh camp towards the old perimeter fence, appears to have lain undiscovered for three decades.
It was abandoned before it was completed - possibly because the inmates found that their planned exit was smack in the middle of the site where H-blocks were being built for the high security prison that opened in 1976.
While the IRA was responsible for many attempts to tunnel out of the jail - the last time in 1997 - several prison sources said the location of the tunnel suggests this may have been a UVF bid to escape.
The demolition crew who took down the Nissen huts at the end of last year figured they were in the vicinity of an old tunnel when they found bags of dirt shoved below the corrugated iron used for the curved roofs of the huts.
"We had no trouble working out what they were from," said Desmond Rodgers, the foreman from contractors John McQuillan and Sons.
The dirt had been placed in small bags sewn from blankets and pillow cases, and shoved into the gaps between the outer skin of the roof and the inner ceiling of several Nissen huts. The outer walls of toilet blocks had also been filled with bags of dirt.
So much dirt was packed into the roofs that the demolition crew was surprised they hadn't collapsed under the weight.
"There was tons of it," said Gavin Smyth, who operates one of the demolition diggers.
"The dirt was all in bags in the roof, like sugar bags, made from blankets and pillow cases."
The crew soon found where the dirt had come from - Gavin's digger fell into the tunnel.
"It was half filled with water," said Desmond Rodgers.
"There was a big roll of cable in there as well," said Sammy McVeigh. "It was used, so they must have stripped it from somewhere else to use it for lights."
The crew filled in the remains of the tunnel for safety reasons, estimating it ran about 60 feet from the huts before ending abruptly.
A Prison Service report on the last tunnel found in the Maze - a 1997 attempt by the IRA - said that "tunnelling attempts were not uncommon" in the old compound. An IRA internee, Hugh Coney, was shot dead by soldiers on November 6, 1974, when he and other republican inmates nearly escaped through a 134-foot tunnel.
The recently discovered tunnel was almost certainly dug after October 1974, when a fire destroyed many of the Nissen huts. The bags of dirt would have been exposed.
But it was probably abandoned before March 1976, when the first H-blocks opened, suggesting it may have been built sometime in 1975.
"This discovery clearly relates to a period during our Troubles past and we sincerely hope these days are consigned to history," a Prison Service spokesman said yesterday.
Demolition of the Maze has reached the prison's perimeter wall, but the H-blocks, which housed thousands of paramilitary prisoners for 25 years, have not yet been taken down.