Macadam

Macadam is a type of road making. It was invented by the Scottish engineer John Loudon McAdam, about 1820.

Construction of the first macadamized road in the United States (1823). In the foreground, workers are breaking stones "so as not to exceed 6 ounces (170 g) in weight or to pass a two-inch (5 cm) ring".

He put crushed stone in shallow, convex layers and compacted thoroughly (squashed it down). Sometimes a layer of stone dust was covered with a cement or bitumin. This keeps the dust and stones together.

Macadam's ideas were built on the ideas of some earlier road engineers, like Trésaguet and Thomas Telford.

The Romans had not used a binding substance like bitumen. Their roads were nevertheless quite long-lasting.