Definition of "ashlar"

The four main spans across the waterway are carried on ashlar piers founded on Memel timber piles.

1949 November and December, “Notes and News: The High Level Bridge, Newcastle”, in Railway Magazine, page 407

And from the choir itself, where the big hoist was working, came the shouts of the men sweating at the great wheel that swung the cut stones skyward, and the men high overhead on the hurdle-walks, waiting to receive the swinging ashlars and guide them into place.

1970, Rosemary Sutcliff, The Witch`s Brat, Red Fox, published 1990, page 83

Even as I babbled, Jock's massy frame filled the doorway, his ill-hewn ashlar head weaving from side to side, eyes blinking at the light.

1973, Kyril Bonfiglioli, Don't Point That Thing at Me, Penguin, published 2001, page 108