The first major vein of silver was found in 1548 in a mine called San Bernabé. This was followed by similar finds in mines called Albarrada de San Benito, Vetagrande, Pánuco and others. This brought a large number of people to Zacatecas, including craftsmen, merchants, clerics and adventurers. The settlement grew over the space of a few years into one of the most important cities in New Spain and the most populous after Mexico City. The success of the mines led to the arrival of indigenous people and the importation of black slaves to work in them. The mining camp spread southwards along the course of the Arroyo de la Plata, which now lies underneath Hidalgo Avenue, the old town's main road. Zacatecas was one of the richest states in Mexico. One of the most important mines from the colonial period is the El Edén mine. It began operations in 1586 in the Cerro de la Bufa. It principally produced gold and silver with most of its production occurring in the 17th and 18th centuries. Spain's silver mining and crown mints created high quality coins, the currency of Spanish America, the silver peso or Spanish dollar that became a global currency.