World Without End is based upon the
Ken Follett novel of the same name, and is the sequel to
The Pillars of the Earth.
It's set 150 years after
Pillars, around the start of the Hundred Years' War and the Black Death. As with
Pillars, it's centred around the fictional town of Kingsbridge.
Very good cast, including Cynthia Nixon, Miranda Richardson, Ben Chaplin, Peter Firth, Charlotte Riley, and Tom Weston-Jones.
There have been four episodes so far. I'm not sure how long it is, but
Pillars had eight episodes.