sentences:  Tikal used Río Azul to secure an important trade route to the Caribbean Sea and challenge Calakmul, its great rival.The city was largely abandoned in the 6th century but saw a resurgence in the Late Classic (c. AD 600–900), probably as a result of repopulation by Kinal.The ruins are situated immediately southeast of the Río Azul ("Blue River") upon a low ridge in the extreme northeast of the department of Petén.