, ▁may ▁have ▁reached ▁a ▁population ▁of ▁over ▁ 2 0 , 0 0 0 . ▁At ▁its ▁peak , ▁between ▁the ▁ 1 2 th ▁and ▁ 1 3 th ▁centuries , ▁C ah ok ia ▁may ▁have ▁been ▁the ▁most ▁popul ous ▁city ▁in ▁North ▁America . ▁Mon k ' s ▁M ound , ▁the ▁major ▁cer emon ial ▁center ▁of ▁C ah ok ia , ▁remains ▁the ▁largest ▁ear then ▁construction ▁of ▁the ▁pre histor ic ▁New ▁World . ▁ ▁These ▁civil izations ▁developed ▁agricult ure ▁as ▁well , ▁bre eding ▁ma ize ▁( c orn ) ▁from ▁having ▁ears ▁ 2 – 5   cm ▁in ▁length ▁to ▁perhaps ▁ 1 0 – 1 5   cm ▁in ▁length . ▁Pot atoes , ▁tom atoes , ▁be ans ▁( gre ens ), ▁p ump kins , ▁av oc ados , ▁and ▁ch oc olate ▁are ▁now ▁the ▁most ▁popular ▁of ▁the ▁pre - Col umb ian ▁agricult ural ▁products . ▁The ▁civil izations ▁did ▁not ▁develop ▁extensive ▁liv est ock ▁as ▁there ▁were ▁few ▁suitable ▁species , ▁although ▁al p ac as ▁and ▁llam as ▁were ▁domestic ated ▁for ▁use ▁as ▁be asts ▁of ▁bur den ▁and ▁sources ▁of ▁w ool ▁and ▁meat ▁in ▁the ▁And es . ▁By ▁the ▁ 1 5 th ▁century , ▁ma ize ▁was ▁being ▁far med ▁in ▁the ▁Mississippi ▁River ▁Valley ▁after ▁introduction ▁from ▁Mexico . ▁The ▁course ▁of ▁further ▁agricult ural ▁development ▁was ▁greatly ▁alter ed ▁by ▁the ▁arrival ▁of ▁Europe ans