This is a very strange Hillfort, being so close to the King’s Seat.
It’s not very big (for a Hillfort) although the banks still stand to an impressive height of 2 metres in places. I would say the interior of the site is about 30 metres across..
As an aside, I picked up a very good guide to the Hill of Tara from the visitor’s centre at Newgrange. A small booklet costing only 50 cents. They do similar booklets for Newgrange, Dowth and Knowth although they were sold out of the Dowth ones when I visited.