Macadam is a type of road construction pioneered by Scottish engineer John Loudon McAdam around 1820. The method simplified what had been considered state of the art at that point. Single-sized aggregate layers of small angular stones are placed in shallow lifts and compacted thoroughly. A binding layer of stone dust, crushed stone from the original material may form; it may also, after rolling, be covered with a binder of fines and small crushed rock.