Nevertheless the slave trade was established and soon attained considerable proportions. It became so flourishing that presently the Spanish government forbade private parties to conduct it save under special charter from the crown and on payment of a considerable royalty on each negro imported. Ostensibly, this was because it was feared that too many negroes might be imported, so as to endanger the security of the colonists, as Velasquez had suggested; but in fact it was largely for the sake of the revenue which thus accrued to the royal treasury. The popular sentiment in Cuba was generally in favor of slavery. It was held that thus only could sufficient labor be secured for the development of the resources of the island. The number of negroes never was as great as some colonists urged that it should be, to wit, three male and three female slaves for every white householder, but it is probable that before the middle of the century the negro population of the island outnumbered the European. Treatment of the slaves was on the whole humane. The negroes were forbidden to carry weapons, or to go about in companies of more than four. They were at times subjected to physical punishment by their masters for misdemeanors, though generally such discipline was required to be administered by the authorities. Miscegenation between Europeans and negroes was prohibited under penalty, and as an additional safeguard against it slaves were required to be imported in equal numbers of the sexes, and all were required to be married. It may be doubted if a similar regard for their sexual morals was ever exhibited elsewhere. There was a provision under which it was possible for industrious and faithful slaves to purchase their freedom, and a considerable number of them did so; after which they became members of the community with almost the same legal rights and privileges as the Europeans.