A metalled road is surfaced with small broken stones, providing a good, strong and long-lasting route for military and civilian traffic.
The road is actually constructed in layers of increasing large stones (going down through a cross section), with each layer being compressed by rolling. The end result is a solid path that can drain cleanly. This method is often used for key strategic and commercial routes between cities and defense points. Tolls are often charged to private users of such excellent roads and turnpikes.
Historically, "metalled roads" were only covered in "tarmac" in 1820, when the idea of using tar to stabilize the top layer was tried by John Loudon McAdam (1756-1836), although "tarmac" itself was not called that until 1901!
Road building produced some other interesting characters, such as Blind Jack of Knaresborough, Yorkshire. Although completely sightless thanks of childhood smallpox, John "Jack" Metcalf (1717-1810) was, at various times, a fiddle player, and army recruiter, and a haulier. When a turnpike was built near his birthplace he used his local experience to create a masterpiece of a road, including a section on a raft of logs across a bog. His blindness was no handicap in bringing road projects in on time and to cost, although he is always at a loss to explain to others how he managed his finances so well.