Although the Portuguese were the first to initiate the slave trade between Africa and Europe in the 15th century, Christopher Columbus, sailing for Spain, was the first to export natives from the Americas across the Atlantic to Europe, and so is generally considered to have established the transatlantic slave trade - as that term is usually understood - in 1492.
The 220-year-old ad, which was placed in Gore's Liverpool General Advertiser, reads: Apply to Lake and Brown: We have on sale by private contract, the remarkably fast sailing ship Metis, Liverpool built, about nine years old, copper fastened on the stocks, is very well found and will carry by the present act, about 185 slaves.