This seems to be about an ancient fort at Rathangan in County Kildare. Anyone seen it?
The Fort of Rathangan
The fort over against the oak-wood,
Once it was Bruidge's, it was Cathal's,
It was Aed's, it was Ailill's,
It was Conaing's, it was Cuiline's,
And it was Maelduin's;
The fort remains after each in his turn-
And the kings asleep in the ground.