Homemade History: Fondant

The fondant we've come to glorify especially in high end cake decorating was once a poor man's answer to sugar. During the Renaissance when sugar was a luxury afforded by the elite, a simple paste of sugar and almonds was formed to sweeten and decorate cakes, thus marking the beginning of this confection's use.
As we know it, traditional fondant is a syrup made from dissolving sugar and corn syrup in water, allowing it to cool into a thick syrup, and perhaps flavoring and dyeing it to sweeten and decorate petit fours. The rolled fondant used for cakes is a combination of gelatin, glucose, glycerin, and powdered sugar. Keep in mind, however, that this combination isn't exactly known for it's sweetness, but rather for it's decorative quality. So, that's why there's a layer of one's favorite butter cream frosting underneath!

Sources: eHow and OChef