I'd pretty much second all of the above, although the Flashman series is a bit past 1300AD it's a gloriously funny read with plenty of action thrown in. I'd also recommend his "
McAuslan" books and "
The General Danced At Dawn". They draw upon his Scots heritage, his student days in Glasgow and his service in a Highland regiment in the war and are riotously entertaining books.
If you're primarily interested in the Roman/Saxon era I'll repeat a recommendation I made in another thread of
Jack Whyte's work. He covers
the Arthurian legend,
the Templars and even has a shot at
William Wallace, which I suppose is reasonable given his
heritage. He's very much in the Cornwell vein.