They also uncovered a substantial new hoard of pottery and further evidence of a large mill with timber beams still intact, but could only partially examine the finds.
It is thought the steps may indicate the location of a washing area but they could also lead to a dungeon, burial chamber or storeroom containing other important artefact.
The 13th century site, which has already yielded the remains of a castle and huge quantities of pottery, coins, tools, personal effects and skeletons, lies in the path of the final section of the M50 motorway in south county Dublin.
Archeologists, who had their excavation deadline extended twice since it started in August 2000, were forced to leave last Friday when the land legally came under the control of the National Roads Authority.
There were emotional scenes as distraught workers who continued digging until the last minute had to be coaxed by colleagues to lay down their tools.
Construction of the road is now in limbo while the Minister for Transport Seamus Brennan considers a plea from An Taisce to re-route the road to allow a full
excavation and preservation of the finds, and a possible compromise proposal from the NRA which would see a section of the motorway raised to preserve some of the structures underneath.
A group of protestors who have been staging a sit-in at the site since last weekend, yesterday warned against further delays in moving to protect the excavations.
While the ‘Carrickminders’ are relieved bulldozers are staying away from the site, they say only their presence is safeguarding the finds.
“We’re beside a public road and there is easy access, and while it’s great to see the number of people interested enough to come down and see the site, it’s a balancing act between trying to allow as many people as want to see the place and keeping discipline and order,” said spokesman Ruadhan MacEoin.
Minster Brennan had been expected to inspect the site before excavations finished. His spokesman said he still intended to make a visit but had not set a date.
The spokesman said the minister was still considering the submissions from An Taisce and the NRA.
Carrickmines supporters, including An Taisce, the Carrickminders and Friends of Medieval Dublin, will hold a series of concerts to highlight the campaign and raise funds. The concerts are in the Temple Bar Music Centre tonight, September 14 and September 20.