The wagons of the Argentine plain have often been described by travellers. They were heavy vehicles, carrying 150, sometimes 180, _arrobes_ (1,725 to 2,070 kgs.), covered with a leather hood stretched on hoops. A long spur decorated with ostrich feathers was balanced on a ring fixed in the roof, and was used to guide the front pair of oxen. An earthenware pot containing water enough for each stage hung between the rear uprights. As a rule, three pair of oxen were yoked to it, one pair being in the shafts. At Corrientes it was necessary to cross the marshes and _esteros_, and a special type of wagon had been evolved. It had a sort of horizontal division forming an upper story, and the driver sat in this. Everywhere, on the Pampa as well as at Corrientes, the wheels were enormous; sometimes, as Darwin says, ten feet in diameter. They were, therefore, able to get through the bad parts. Mud was, as a matter of fact, the worst enemy of the convoys. The soil of the Pampa is clayey and soft in the districts near the river. As the road was not limited in width, the wagons turned to the right or the left when the ruts became too deep, and the track in time covered a broad belt of ground. This, however, could not be done in the vicinity of towns, where the traffic was concentrated. Buenos Aires came to be surrounded by formidable quagmires that dried up only in the summer. The paving of the streets and environs was becoming a problem of national importance when the construction of the railway began. Wagons did not travel singly. The _tropero_, or contractor for transport, organized caravans. In peaceful districts, where no military escort was required, the convoys could be split up; they consisted, as a rule, of from fifteen to fifty wagons. Besides the six oxen yoked to the wagon, there had to be others for relief as well as horses for the staff. Usually they allowed ten oxen to each wagon; in exceptional cases twenty.[111] The convoy to the salt-lakes in 1778 had no less than 12,000 oxen to 600 wagons. There was a driver to each wagon, but there had also to be drivers for the starting animals, and carpenters to make repairs. The leader of the caravan, the _capataz_, was generally a master-carpenter. He looked after the interests of the _tropero_. There were about three men to each wagon. The _carreros_ were an original type, nomadic, and very different in costume and character from the _gauchos_ (breeders) of the plain. At the close of the eighteenth century Buenos Aires had more than a thousand wagons employed in the traffic to Mendoza and Tucuman (Borrero).