This Pacific route was the alternative to the trip west across the Indian Ocean, and around the Cape of Good Hope, which was reserved to Portugal according to the Treaty of Tordesillas. It also avoided stopping over at ports controlled by competing powers, such as Portugal and the Netherlands. From the early days of exploration, the Spanish knew that the American continent was much narrower across the Panamanian isthmus than across Mexico. They tried to establish a regular land crossing there, but the thick jungle and malaria made it impractical.