The encierro is usually composed of the six bulls to be fought in the afternoon, six steers that run in herd with the bulls, and three more steers that follow the herd to encourage any reluctant bulls to continue along the route. The function of the steers, who run the route daily, is to guide the bulls to the bullring. The average speed of the herd is 24 km/h.
The length of the run is 875 meters. It goes through four streets of the old part of the city (Santo Domingo, Ayuntamiento, Mercaderes and Estafeta) via the Town Hall Square and the short section "Telefonica" just before entering into the bullring through its callejon (tunnel). The fastest part of the route is up Santo Domingo and across the Town Hall Square, but the bulls often became separated at the entrance to Estafeta Street as they slowed down. One or more would slip going into the turn at Estafeta, resulting in the installation of anti-slip surfacing, and now most of the bulls negotiate the turn onto Estafeta and are often ahead of the steers. This has resulted in a quicker run. Runners are not permitted in the first 50 meters of the encierro, which is an uphill grade where the bulls are much faster.