The Collaborative International Dictionary of English v.0.48:
Rubble \Rub"ble\, n. [From an assumed Old French dim. of robe
1. Water-worn or rough broken stones; broken bricks, etc.,
used in coarse masonry, or to fill up between the facing
courses of walls.
Inside [the wall] there was rubble or mortar.
2. Rough stone as it comes from the quarry; also, a
quarryman's term for the upper fragmentary and decomposed
portion of a mass of stone; brash. --Brande & C.
3. (Geol.) A mass or stratum of fragments or rock lying under
the alluvium, and derived from the neighboring rock.
4. pl. The whole of the bran of wheat before it is sorted
into pollard, bran, etc. [Prov. Eng.] --Simmonds.
Coursed rubble, rubble masonry in which courses are formed
by leveling off the work at certain heights.