According to Wikipedia "Fortified wine is wine to which a distilled beverage (usually brandy) has been added. When added to wine before the fermentation process is complete, the alcohol in the distilled beverage kills the yeast and leaves residual sugar behind. The end result is a wine that is both sweeter and stronger, normally containing about 20% alcohol by volume (ABV). The original reason for fortifying wine was to preserve it, since ethanol is a natural antiseptic. Even though other preservation methods exist, fortification continues to be used because the fortification process can add distinct flavors to the finished project."
Madiera comes from the Island of Madiera which is a Portuguese possession. The wines used to be aged as balast in sailing ships where a couple of trips to the equator did the trick, Today the wine storage is simply heated to 40-46 degrees C for six months. The four different types of madfiera are bamed after the grapes that produce them. Sercial is the best of the dry madiera's. It is a light dry wine with a superb nose. Verdelho is a little sweeter. It was taken with cake during the Victoian era. Bual is a russet coloured dessert wine with a distinctive bouquet. Malmsey from the Malvoisie grape is a rich luscious wine excellent to continue the memory of a great dinner.
Marsala comes from the north-west of Sicily and can be sweet (dolce) or dry (secco). It comes in three colours: Ambra (amber), Oro (gold) and Rubino (ruby) which comes from red grapes. It is also classified by age: Fine (aged 1 year), Superiore (2 years), Superioire Riserva (4 years), Vergine (5 years), Staravecchio (10 years). There are also Solera Marsalas. The fermentation of the grape must is stopped at the desired level of sweetness by the addition of brandy. The alcohol content is from 16%-20%.