at Chester and Bristol supplied by Danish, Mercian, and Welsh raiding of one another's borderlands. At the time of the Domesday Book, nearly 10% of the English population were slaves. William the Conqueror introduced a law preventing the sale of slaves overseas. According to historian John Gillingham, by 1200 slavery in the British Isles was non-existent. Slavery had never been authorized by statute within England and Wales, and in 1772, in the case Somerset v Stewart, Lord Mansfield declared that it was also unsupported within England by the common law. The slave trade was abolished by the Slave Trade Act 1807, although slavery remained legal in possessions outside Europe until the passage of the Slavery Abolition Act 1833 and the Indian Slavery Act, 1843. However, when England began to have colonies in the Americas, and particularly from the 1640s, African slaves began to make their appearance in England and remained a presence until the eighteenth century. In Scotland, slaves continued to be sold as chattels until late in the eighteenth century (on the second May, 1722, an advertisement appeared in the Edinburgh Evening Courant, announcing that a stolen slave had been found, who would be sold to pay expenses, unless claimed within two weeks). For nearly two hundred years in the history of coal mining in Scotland, miners were bonded to their "maisters" by a 1606 Act "Anent Coalyers and Salters". The Colliers and Salters (Scotland) Act 1775 stated that "many colliers and salters are in a state of slavery and bondage" and announced emancipation; those starting work after 1 July 1775 would not become slaves, while those already in a state of slavery could, after 7 or 10 years depending on their age, apply for a decree of the Sheriff's Court granting their freedom. Few could afford this, until a further law in 1799 established their freedom and made this slavery and bondage illegal. The Byzantine-Ottoman wars and the Ottoman wars in Europe brought large numbers of slaves into the Islamic world. To staff its bureaucracy, the Ottoman Empire established a janissary system which seized hundreds of thousands of Christian boys through the devşirme system. They were well cared for but were legally slaves owned by the government and were not allowed to marry. They were never bought or sold. The empire gave them significant administrative and military roles. The system began about 1365; there were 135,000 janissaries in