RAMPS - Heavy cannon on massive wooden carriages were hauled up and down the ramps which lead to the various levels of San Cristobal by sheer manpower using levels, blocks, and tackle. To avoid animal wastes contaminating the water supply which comes from rainwater collected from the surfaces of the fort by channels into underground cisterns, no horses, oxen, or mules were allowed inside the walls.   Fort San Cristóbal | El Morro | City Walls | Cañuelo