The Isthmus of Tehuantepec, a region located in the south of Mexico, is the shortest distance between the Atlantic and Pacific oceans in all the country. Only 220 kilometers separate the two oceans. In the first half of the 16th century, Spanish conquerors put great effort into finding a strait that would connect the two oceans. This meant that, in the conquest explorations of the 16th century, this region was used as an inter-oceanic passage, making approximately two thirds of the journey along the mighty river Coatzacoalcos and the rest overland.
Click here for original story, Cartography shows that the Isthmus of Tehuantepec was used as an inter-oceanic passage in the 16th century
Source: Phys.org