The Latinized name Darius may go back to the name used by the Celtic tribes who inhabited the area before Roman times: the Celtic root is *dubro-. In modern Welsh, dŵr is "water," as well as dour in modern Breton with cognate dobhar in Irish. In Roman times, the river was personified as a god, Durius. Another long-established derivation suggests that the name Douro comes for the Portuguese word for "golden". The Douro vinhateiro (winegrowing), an area of the Douro Valley in Portugal long devoted to vineyards, has been designated by UNESCO as a World Heritage Site. Traditionally, the wine was taken downriver in flat-bottom boats called rabelos, to be stored in barrels in cellars in Vila Nova de Gaia, just across the river from Porto. In the 1960s and 1970s, dams with locks were built along the river, allowing river traffic from the upper regions in Spain and along the border. Nowadays Port wine is transported to Vila Nova de Gaia in tanker trucks. In 1998, Portugal and Spain signed the Albufeira Convention, an agreement on the sharing of trans-boundary rivers to include the Douro, Tagus, and Guadiana. The convention superseded an original agreement on the Douro, signed in 1927, that was expanded in 1964 and 1968 to include tributaries.