There were two kinds of legal slaves, those made by capture in war, and those by birth. Slaves by purchase, taken from Africa and the Caucasus, were not recognized by law, but nevertheless such slavery existed.[30] Brigands also seized foreigners from time to time and sold them as slaves. Prisoners of war lost their civil liberty according to Islamic law. The Prophet repeatedly enjoins their destruction.[31] According to the Turkish code, the sovereign might perpetuate their captivity, or free them to pay tribute, or cause them to be slaughtered, if more expedient. The exceptions to this law were the cases of any orthodox Moslems who might fall into Turkish power, and the case of the Tatars of the Crimea, who were Shiites, or heretic Moslems, and who were enslaved.[32] Prisoners of war formed two classes of slaves, prisoners of the state, and private slaves. To the first class belonged all soldiers and officers, and a fifth of the rest of the slaves, or their value. Of these some were exchanged or resold after the peace, others were employed in the Serai or given away. Some were handed over to public works, especially to the admiralty, where they were confounded with criminals and condemned to hard labor. To the second class belonged all the prisoners not given to the sultan, including those captured by the soldiers. These were generally sold. Merchants would purchase them in the camps, and sell them all over the Empire. These slaves taken in war were far the greater number of slaves in the Empire; many were enfranchised before they had children, and children of one free and one slave parent were themselves born free. The adoption of Islam after captivity did not free the slave. The power of the master was absolute over the person, children and property of his slaves. He might sell, give, or bequeath them, but he might not kill them without some reason. As a corollary of this power, the master had full responsibility for his slave; he must support him, pay his debts, stand behind him in any civil affair, and give consent to his holding of property. A slave might not act as a witness nor as a guardian. He was entirely dependent on his master.