As chapter 2 continues, Edwards does actually get to ring-forts.
She discussed the difficulties of dating early medieval settlements. After all, it’s not as though early medieval builders left nice dated cornerstones on their structures. Even if they had, the dates might well be a local king ‘s regnal year rather than an A.D. date–not necessarily helpful.
Objects found in the area can help with dating, but of course that’s it’s own site of difficulties. It turns out that a good place to live in Neolithic times is still a good place to live in early medieval times and still a good place to live by early modern times. There are sites in Ireland that have been continuously occupied for 6000 years (Lough Gur, for instance). Being able to date an object found at a particular location does not necessarily allow you to date the construction there.
So, with all those academic caveats behind us, you might be asking, what the heck is a ring-fort anyway?
The simplest definition is an enclosed homestead. The enclosure might be an earthen bank or a stone wall, and there might be ditch in front of the wall. They’re circular-ish usually, hence the name. They are defensive in nature, but probably more to ward off animals and perhaps the stray robber rather than to repel a concerted attack. These appear in The Last Abbot of Linn Duachaill both at Evgren’s home, a mostly abandoned ring-fort, and the monastery itself, which has a ditch, an earthen bank, and thorny bushes atop the bank.