In the 17th century, two cakes were made, one for the bride and one for the groom. The groom's cake would die out and the bride's cake become the main cake for the event. When the two cakes were served together, the groom's cake was typically the darker colored, rich fruit cake and generally much smaller than the bride's cake. The bride's cake was usually a simple pound cake with white icing because white was a sign of virginity and purity.
You should use a recipe specifically designed to be a wedding cake as it will ensure that it is sturdy enough and that it makes the right amount of batter and icing. For a three-tier cake, you need to make three cakes of 12", 9" and 6", as well as a massive amount of icing. Most three-tier cake recipes have a step-by-step schedule for when you will need to bake and assemble each part.