On the day of Chimalpopoca's coronation in 1417 (some sources say 1416 or 1418), his brother Tlacaelel I was named high priest. From this point on the ecclesiastical and governmental offices among the Aztecs were separate. When he assumed the throne at age 20, Tenochtitlan was a tributary of the Tepanec city of Azcapotzalco, which was ruled by his grandfather Tezozomoc. This alliance, and the Mexicas' position within it, was strengthened by Tenochtitlan's loyalty during Tezozomoc's 1418 war with Ixtlilxochitl I of Texcoco. The conquered city was granted to Tenochtitlan as a tributary. Chimalpopoca also had a causeway constructed to Tlacopan. The causeway contained openings spanned by wooden bridges, which were removed at night. Also during his reign he dedicated a stone for sacrifices in the Tlacocomoco section of Tenochtitlan. To him is attributed the conquest of Tequizquiac.