1824, named for inventor, Scottish civil engineer John L. McAdam (1756-1836), who developed a method of leveling roads and paving them with gravel and outlined the process in his pamphlet "Remarks on the Present System of Road-Making" (1822). Originally the word meant road material consisting of a solid mass of stones of nearly uniform size laid down in layers (McAdam did not approve of the use of binding materials or rollers). The idea of mixing tar with the gravel began 1880s.