This lasted until approximately 900 AD, when the Classic Maya civilization collapsed. The Maya abandoned many of the cities of the central lowlands or were killed by a drought-induced famine. The cause of the collapse is debated, but the drought theory is gaining currency, supported by evidence such as lakebeds, ancient pollen, and others. A series of prolonged droughts in what is otherwise a seasonal desert is thought to have decimated the Maya, who relied on regular rainfall to support their dense population.