express authority

Augustus himself took charge of those near Rome, and appointed two men of prætorian rank to pave the roads: at the distance of five or six miles houses were built, each of which was constantly provided with forty horses; but these could only be used in the public service, except by particular and express authority.

A General History and Collection of Voyages and Travels - Volume 18 Historical Sketch of the Progress of Discovery, Navigation, and Commerce, from the Earliest Records to the Beginning of the Nineteenth Century, By William Stevenson William Stevenson 1784