Geography in Mexico has an interesting but little known history. Geographers in the past made important contributions both to the recognition of the country and to the advancement of this discipline. One example is the definition of Mexico's borders. In Mexico, as in Latin America, the definition of borders occurred in the nineteenth and twentieth centuries. The scientific work developed by the geographic engineers of the Mexican border commission allowed for the placement of landmarks that separate Mexico from its neighboring countries. This allowed the conformation of the National territory. The purpose of this research is to answer the question: How was the border that separates Mexico from Guatemala and Belize demarcated? In order to answer this question, documents and maps contained in Mexican Historical Archives were analyzed. This paper provides elements to the History of the Mexican Geography.