Through the ages grain has come to symbolize fertility and the evolution of wedding cakes can be traced back to this belief.  During the ancient Roman times a loaf of barley bread was baked, the groom would eat a little of it, and break the rest over his brides head as a symbolism of fertility.  Folklore has it that the more crumbs that was produced the more children the couple would have.  Guest would gather up the crumbs assuming it would bring them good luck.  

Over time larger and more loaves were used so all guest could share in the good fortune. In medieval England, the bread were described as flour-based sweet foods as opposed to the description of breads which were just flour-based foods without sweetening. The presence of the cake was included in many celebratory feasts.. There are tales of a custom involving stacking small sweet buns in a large pile in front of the newlyweds. The couple would then attempt to kiss over this pile, with success being a sign of many children in the couple's future. 

More recently this tradition evolved the bride and groom kissing over a pile of small cakes and then as time went on these small cakes were then joined together with icing and producing the tiered cake with icing.