The principal cultigen was maize, but the Maya grew squash, beans, chili peppers, amaranth, manioic and cocao. One of the main methods of farming involved clearing the forest and burning the debris to create fields, called milpas, that were planted just before the rainy season began. Such slash-and-burn agriculture is inefficient, since any single field cannot be planted for more than two or three years before it is exhausted, and from very early times, the Maya developed intensive farming methods. Land on slopes or near gullies was often terraced, but raised-fielding farming, the most widespread and effective method, was practiced along slow-moving rivers and in swampy areas. Canals were cut between fields and their bottom matter placed on the prepared fields to enrich the soil. Periodically, when the canals were dredged, the bottom detritus was again used to fertilize the fields. The attributes associated with this type of farming—the chest-deep water, the water-lilies that grew in the canals, the fish that lived in them, the birds that ate both plant and fish and the caiman that ate yields form milpa and raised-field production were domestic gardens and husbandry of the forest. The fruit imagery incorporated into Maya art, as on the sides of Pacal’s sarchophaus at Palenque, indicates that they either raised or harvested from the forest quantities of avocados, chico zapote fruit, guanavana, nancé, cacao and possibly also ramon nut or breadfruit. Other crops included cotton, used for light cloth, and sisal, used for heavy cloth and rope.