Callao became the main port for Spanish commerce in the Pacific after its founding by Spanish colonists in 1537. The origin of its name is unknown; both Indian (particularlyYunga, or Coastal Peruvian) and Spanish sources are credited, but it is certain that it was known by that name since 1550. Other sources point to the similarity with the Portuguese word calhau [pebble], having a similar sound.
At the height of the Viceroyalty, virtually all goods produced in Peru, Bolivia, and Argentina were carried over the Andes by mule. Wikipedia