 Although it was more expensive to purchase a slave than it was to employ a freeman, the sparse population and the lack of free labor made the purchase of a slave a favorable capital investment.The number of black slaves in Portugal given by contemporary accounts argue that Lisbon and the colonies of Portugal averaged a maximum of 10% of the population between the 16th and 18th centuries, but these numbers are impossible to verify.Most slaves in Portugal were concentrated in Lisbon and to the south in the Algarve.