An estimated 100,000 slaves were imported before the year 1600. The Spanish settlements of Cauca Valley which were known for its richness in gold and North Antioquia benefited most from this steady supply slaves since, by 1560, the Indian laborers were no longer easy to come by. Slaves were regarded as an important asset since they were cheap and the work they were required to do was labor-intensive. Women were not spared either from the back-breaking work at the open-cast mines. Both male and female miners worked in groups called cuadrillas (or gangs), each led by a captain. They were also in agriculture and looked after cattle in the haciendas in Cauca Valley. In as much as they were also used as artisans, domestic servants and laborers in large haciendas in the Caribbean plains, their main occupation was mining. According to Wade, the harshness with which slaves were treated varied according to the epoch and the region in which they were posted. However, some of them were given the opportunity to buy their own freedom, especially the women and children. Most slaves were also able to farm, mine or sell goods for their own benefit on a specific day in a week. Some slave owners even granted their own slaves freedom. Sexual relationships between white men and black women led to a new ‘race’ of people who could neither be classified as being white, slave nor Indian and constituted about 60% of the population in New Granada by the 1770s. Some slaves fought for their own freedom, perhaps when the working conditions became unbearable and fled to uncontrolled areas where they formed villages and fortified them for their defense against the Spanish military. The first revolt took place in 1530 in Santa Marta, Colombia. The slaves completely burnt down the town. Even after it was rebuilt in 1531, it was again burnt down in 1550 in another slave revolt.