The league expresses the distance a person, or a horse, can walk in 1 hour of time.
The Spanish League or Legua was originally set as a fixed unit of distance of 5000 varas, about 2.6 miles or 4.2 km. Officially the league was abolished by Philip II of Spain in 1568, but it is still in use unofficially in parts of Latin America, with exact meaning varying in different countries.
In Argentina a league is a distance of 5 km.
In Yucatan and other parts of rural Mexico the league is still commonly used in the original sense of the distance that can be covered on foot in an hour, so that a league along a good road on level ground is a greater distance than a league on a difficult path over rough terrain.
See Historical weights and measures for various definitions of the league.