This is a site that would bear further investigation. The top of Barretstown Hill is surrounded by a ditch and bank close on a kilometre in circumference. The bank and ditch are overgrown with hawthorn trees.
An archaeological survey of Co. Kildare mentions four round barrows here but it's hard to make them out. Are they inside the enclosure? Would that be likely, presuming that the enclosure was a habitation site? They're marked on the map as being at the south end of the top of the hill and this puts them inside. However, there are a great many earthworks to the north of the hill, scooped out quarries with small, barrow-like mounds that may be of a more modern vintage.
Barretstown Hill is the highest point for miles around and would have been easily defended. So where are the barrows?