Monument 55, just west of the visitor centre, was complete and in perfect condition when Petrie saw it in 1837, but the monument seems to have been dismantled soon afterwards for use as building materials.
Tomb No. 55 at Carrowmore, according to Wood-Martin's Rude stone monuments of Ireland, was, in the 19th century, completely covered with field stones.
"This circle, with its cromleac, which Petrie states was, in 1837, tolerably perfect, is now so covered with stones-the clearing of fields-which had been thrown on it, that a description is impossible"
In order to determine whether a megalithic tomb was hidden under the heap of stones, removal of the covering material with the help of light machinery took place during the 1998 season. It was found that the covering material consisted of field stones, thrown up in recent times. Modern glass, fragments of clay pipes and porcelain were found down to the very bottom level of the cairn. On ground level three gneiss boulders were found, placed close together in a slightly rounded shape, but there were no visible remains of any chamber.
To determine whether the boulders were also thrown into the heap from the surrounding fields or were the remains of a boulder circle of a destroyed megalithic tomb a six meter-long test-trench was laid out from the boulders towards the north. In the first layer more modern material was found, but in the second layer large amounts of cremated human bones were found, together with fragments of mushroom-headed antler pins and bone and stone beads.
Radiocarbon samples were taken from among the cremations. One dated sample reveals that the tomb was in use in around 3800 BC. An area of eight square meters was opened, and a full excavation is planned for the 1999 season.
Situated to the north of the preceding (No. 54) and close to the road. It is the external chain of circles which commenced with No. 1. From Colonel Wood-Martin's plan it would appear that this circle is south-west of LXVI (dolmen-circle).
"This circle is more perfect, but of the stones have been removed to form a garden wall. The cromleac is perect, but covered with stones. The place of any intermediate circles which may have existed (between this and No. 1, so as to make the chain perfect) have been occupied by the road and houses on either side."
- Petrie, 1837.