sentences:  During the site's Late Classic resurgence the rural population density in the once-peripheral BA-20 group reached approximately 300/km2 (777/square mile).Between AD 692 and 830 the total population at Río Azul once again peaked at around 3500, with 2500 of these in the BA-20 zone.An individual nicknamed Six Sky by archaeologists was a prominent ruler of Río Azul in the early 5th century AD.