What are those old Irish guard towers called?

I went to Ireland a few years ago on a school trip and we passed a lot of ruins that looked like little mini castles. Our guide called them _____ houses. It sounded like “tara” houses, but I’m pretty sure that wasn’t it. Does anyone know what they’re called? Here’s a link to a picture of one—> http://www.23hq.com/chubacca/photo/4646922?album_id=4646888