The streets of Pompeii vary greatly in width. The widest is Mercury Street, the continuation of which near the Forum has a breadth of nearly 32 feet. Next come Abbondanza and Nola streets, the greatest width of which is about 28 feet; the other streets and thoroughfares vary from 10 to 20 feet. With unimportant exceptions, broad and narrow streets alike are paved with polygonal blocks of basalt, which in laying were fitted to one another with great care; on both sides are raised sidewalks, with basalt or tufa curbing. The sidewalks in some places are paved with small stones, elsewhere are laid with concrete, or left with a surface of beaten earth. As there is no uniformity, the sidewalk varying in front of adjoining houses, it is clear that the choice of materials was left to individual owners of abutting property. The limits of ownership are often designated by boundary stones, laid in the surface of the walk. Broad ruts, worn by wheels, are seen in the pavement, shallower in places where the basalt flags, cut from the lowest stratum of the stream of lava, are particularly hard; deeper wherever there are blocks quarried nearer the surface. Only the principal streets were wide enough to allow wagons to meet and pass; elsewhere drivers must have waited at a corner for a coming team to go by. It seems likely that driving on the streets of the city was forbidden, wheeled vehicles being used only for traffic; people who wished to ride availed themselves of litters. At various places along the thoroughfares, but particularly at the corners, large oblong stepping stones with rounded corners were set in the pavement at convenient distances for those wishing to cross, the surface being on a level with the sidewalk. The number varied according to the width of the pavement; in the broadest streets as many as five were used. They were arranged always in such a way as to leave places for the wagon wheels. It is not difficult to understand how Pompeian drivers guided their teams past them; draft animals were attached to the wagon by means of a yoke fastened to the end of the pole, and, as there were no tugs or whippletrees, they had a greater freedom of movement than is allowed to modern teams.