In Bordeaux, the original wines made before the 19th century were basically field blends. That is, they harvested all the grapes together without sorting by varietal and vinified the lot together. Sometimes it would result in a pale red called a clairet, which the British called claret – a term they still use today for any Bordeaux red.
The red grapes in the blend were usually Cabernet Sauvignon, Merlot along with Cabernet Franc, Petit Verdot and Malbec. They still blend these grapes together but only after fermentation and ageing them separately by grape variety. The blend is usually made just prior to bottling. Blending gives the final wine more depth and complexity.
The Bordeaux blend has been a huge success and has inspired imitators worldwide, particularly in California and Washington.