The tradition of buying and selling in temporary markets set up either on a regular basis (weekly, monthly, etc.) is a strong feature in much of Mexican culture and has a history that extends far back into the pre-Hispanic period. It was the most important form of commerce in the pre-Hispanic era, and after the Spanish Conquest, the Europeans mostly kept this tradition intact. Market areas have been identified in ruins such as El Tajín in Veracruz, and a number of pre-Hispanic towns were initially founded as regional markets, such as Santiago Tianguistenco and Chichicastenango, Guatemala . The word derives from the Nahuatl word 'open air-market', from 'to trade, sell'. The most important markets, such as the one in Tlatelolco, were set up and taken down every day of the week. This market served about one fifth of the population of Tenochtitlan (Mexico City) before the Conquest and had its own governing system, which included a panel of twelve judges to resolve disputes. Today, one of the most visited exhibits in the National Museum of Anthropology is the model of the pre-Hispanic market such as the one in Tenochtitlan.