Tara was the political center of Ireland, Uisneach was the spiritual one.
Tara was the seat of Kings, while Uisneach was the seat of the priests. It
was crucial (according to Rees and Rees) that these two centers remain in
perfect balance. If one center gained more power, chaos would ensue.
One such example (citing from memory, we all know by now how well I do with
THAT) is that the fire at Tara was not lit until the fire at Uisneach was
sighted. Not doing so would throw off the balance of power.
Which makes you wonder again about current politicans with no spiritual
center, and the chaos some of THEM cause . . .