an ethnic group, the Tepanecs; arrived in the Valley of Mexico in the late 12th or early 13th centuries; their leader, Acolnahuacatl, took over leadership of Azcapotzalco; their subsequent leader Tezozomoc of Azcapotzalco ruled at the height of their influence, especially extending it over such places as the Valley of Toluca and in Morelos (see attestations)