The history of wedding cakes is fascinating and dates back to the Romans. Though they did not use the type of cakes we are familiar with today. They actually used bread as the wedding cake. It also had a number of rituals associated with it down to the breaking of the bread above the couple or sometimes just above the groom.
During the middle ages wedding cakes were simple biscuits or scones. Wedding cakes did not begin to resemble the wedding cake we know today until about seventeenth century France, of course leave it to the French, when bakers started stacking wheat buns and coating them with icing.
The traditions and the histories are both fascinating and varied. Please google for more history of the wedding cake.