For the 1855 Exposition Universelle de Paris, Emperor Napoleon III requested a classification system for France's best Bordeaux wines which were to be on display for visitors from around the world. Brokers from the wine industry ranked the wines according to a chateau's historical reputation and trading price, which at that time was directly related to quality in the market and divided these top wineries into 5 classifications. The result was the Bordeaux Wine Official Classification of 1855.
The wines were ranked in importance from first to fifth growths (crus). The white wines, then of much less importance than red wine, were limited to the sweet varieties of Sauternes and Barsac and were ranked only from first growth to second growth.

 

With several thousand different Châteaux producing their own wines in Bordeaux, to be classified was to carry a mark of high prestige.
The best of the best wines were assigned the highest rank of Premier Cru; only four wines, Château Latour, Château Lafite Rothschild, Château Margaux and Château Haut-Brion were deemed worthy. Of all the 61 great classified wines, all but one came from the Medoc region. The exception was Château Haut-Brion, produced in Graves.
The 1855 list remained unchanged for over a hundred years until Mouton Rothschild was promoted to Premier Cru status in 1973, after decades of lobbying by its owner, Baron Philippe de Rothschild. Of lesser importance, in 1988 Château Haut-Brion was changed in appellation from Graves to Pessac-Leognan to represent changes caused by the urbanization of areas surrounding Bordeaux.
Only twice since the 1855 classification has there been a change, first when in 1856 Château Cantemerle was added as a fifth growth (originally omitted due to a complicated history - ownership) and in 1973, when Château Mouton Rothschild was elevated from a second growth to a first growth. A third, but less known 'change', is the removal of Château Dubignon, a third growth that was absorbed into the estate Château Malescot St. Exupery.