FIRST Double Jeopardy 2.0! (4/26)

Okay, new game plan. Seeing as my “15 Questions in 5 Days” gimmick didn’t go over too well with the Powers That Be, we are forced to eliminate the 16th-25th on our schedule. Questions will now be at their regular times.

For 600, during the Norman conquest of Wales, this was the last stronghold of the Welsh princes against the kings of England. Remember to PM me your answer in the form of a question wtihin 50 minutes.