Until the mid 20th century, beef cattle were often sent to market "on the hoof". Cowboys or drovers would herd the cattle along the roads or on trails to the cattle markets in big towns or cities, or to railway stations where they would be loaded and shipped to these towns or cities. In Australia, sometimes the cattle would travel for hundreds of miles along roads known as 'Traveling Stock Routes'. Big herds would have thousands of 'heads of cattle'. (Cattle are counted by the "head".) Nowadays cattle are usually sent to the market in huge lorries known as road-trains. In North America, cattle are sent to auction marts, slaughter plants or other farms or ranches by large semi-trucks called cattle liners.