Hohokam is a Pima word meaning "the ones who have gone", referring to their ancestors in Central Arizona. If the Pima and Tohono O'Odham tribes are considered descendants of the Hohokam, they are among the most stable indigenous societies on earth, having remained in Central and Southern Arizona for over two-thousand years. The first Hohokam arrived in what is now Northern Mexico in approximately 0 A.D. The civilization reached its zenith over a thousand years ago, when the population neared 1 million and major Hohokam cities existed in the vicinity of present-day Phoenix and Casa Grande, constructed around the confluence of the Gila and Salt Rivers was later dug out and contributed to the phenomenal growth of Phoenix after 1890. They disappeared inexplicably around 1400 A.D.