The central purpose of geographical delimitation of a wine area, typically into a controlled appellation, is to establish a distinctive identity for the wines produced within it, and provide a means whereby the provenance of those wines can be guaranteed. It is based primarily upon the assumption that different environments give rise to wines of different character (see terroir).
Since classical antiquity, wines from certain regions tended to be called after the area of their production, with many gaining particularly high reputations (falernian, for example), but the first legal vineyard delimitation may well have been that of chianti, Pomino, and carmignano in 1716 by Cosimo III de’ Medici, Grand Duke of Tuscany, in a document which further states that penalties will be incurred if any wine makes a false claim to be from those demarcated regions. The douro Valley of northern Portugal was famously first delimited in 1756, associated with the establishment of the Companhia Geral da Agricultura das Vinhas do Alto Douro. During the 18th century, there had been many disputes over the sources and qualities of wines exported from Oporto (see port), as well as conflicts between foreign wine shippers and the Portuguese growers, and the formation of the Companhia Geral with strictly defined areas of operation was designed to remedy the situation. At the heart of this legislation was the establishment of a specific area in the upper Douro Valley from which farmers were able to obtain higher prices for their wines compared with those produced elsewhere.