▁located ▁on ▁the ▁eastern ▁side ▁of ▁the ▁pla za . ▁It ▁had ▁an ▁ear then ▁r amp ▁that ▁gave ▁access ▁to ▁the ▁sum mit ▁from ▁the ▁north ▁side . ▁Here , ▁at op ▁Brown ▁M ound ▁and ▁the ▁other ▁m ounds , ▁the ▁town ' s ▁inhabitants ▁carried ▁out ▁complex ▁rit uals , ▁centered ▁especially ▁on ▁the ▁death s ▁and ▁bur ial s ▁of ▁S pi ro ' s ▁powerful ▁r ul ers . ▁ ▁Arch ae olog ists ▁have ▁shown ▁that ▁S pi ro ▁had ▁a ▁large ▁resident ▁population ▁until ▁about ▁ 1 2 5 0 . ▁After ▁that , ▁most ▁of ▁the ▁population ▁moved ▁to ▁other ▁towns ▁nearby . ▁S pi ro ▁continued ▁to ▁be ▁used ▁as ▁a ▁regional ▁cer emon ial ▁center ▁and ▁bur ial ▁ground ▁until ▁about ▁ 1 4 5 0 . ▁Its ▁cer emon ial ▁and ▁mort u ary ▁functions ▁continued ▁and ▁seem ▁to ▁have ▁increased ▁after ▁the ▁main ▁population ▁moved ▁away . ▁ ▁The ▁Great ▁Mort u ary ▁ ▁Craig ▁M ound ▁– ▁also ▁called ▁" The ▁S pi ro ▁M ound " ▁– ▁is ▁the ▁second - larg est ▁m ound ▁on ▁the ▁site ▁and ▁the ▁only ▁bur ial ▁m ound . ▁It ▁is ▁located ▁about ▁ ▁sout heast ▁of ▁the ▁pla za . ▁A ▁cav ity ▁created ▁within ▁the ▁m ound , ▁about ▁ ▁high ▁and ▁ ▁wide , ▁allowed ▁for ▁almost ▁perfect ▁pres ervation ▁of ▁frag ile ▁artifact s ▁made ▁of ▁wood , ▁con ch ▁shell , ▁and ▁co pper . ▁The ▁conditions