In the past, different types of animals were used to pull the plow, the choice depending on the strength needed, the desired pace and the nature of the terrain. Oxen were among the most commonly used animals, being strong, robust and with a slow and sure gait. Sometimes cows or mixed pairs were also used. In more recent times, although less frequently, horses, mules or donkeys were used, either singly or in pairs, depending on the need. With the introduction of agricultural tractors, animal traction was replaced by mechanical traction.