That's what I love about this Board. While I had long known about The Ple of Irish history, I did not that there had been so many others, including another English Pale, around Calais. Here's a link to a Britannica article on pales in general
http://208.154.71.60/bcom/eb/article/3/0,5716,59523+1,00.html

And here's a link to map showing The Pale in mediæval Ireland
http://www.irelandstory.com/maps/historical/map1450.gif