This is a Wedgwood copy of a famous ancient Roman vase made about 5-25 AD. The original Roman vase is made from dark glass with a lighter layer of glass over the top. The top layer of glass on the Roman vase was cut away to form the decoration. Wedgwood's vase is made in black and white jasper. The white top layer of jasper has been pressed into moulds and then applied to the black vase. Technically, it was a very difficult vase to make and Wedgwood only made 30 copies between 1790 and 1795.
It is called the Portland Vase after the Duchess of Portland who purchased the original vase in 1784 from Sir William Hamilton. He had brought the vase back from Italy the previous year.