Medieval Wedding Cakes

In early medieval times, various symbols of fertility were thrown at the bride for good luck and prosperity. This could be anything from grains of wheat (or rice!), breadcrumbs, or cakes made of wheat. In some places, she (or the groom) would take a bite from the cake and crumble the rest over her head for good luck. Guests would then scramble around her feet to pick up the crumbs, in order to absorb some of that good luck.

Later, the tradition evolved into the bride pushing pieces of her wedding cake through her ring to the guests. Those in attendance would take that piece of cake home to place under their pillows for, again, good luck.
Another custom involved stacking various baked goods (pies, biscuits, cakes, scones etc) into the tallest mound they could manage.
If the bride and groom could kiss over the top without toppling the pile, they were assured a lifetime of prosperity.

Later (17th Century), "bride pie" became popular, which varied from sweet breads to mince pies or even mutton pie. A glass ring was often hidden within it, and whichever woman found it was meant to become the next bride.

Modern-day traditions involve throwing confetti, a tiered wedding cake and throwing the bouquet, each of these is a photo-opportunity. The cutting of the cake is a focal point at any reception today, a tradition rooted in history when the first cut was made by the bride to ensure the marriage would be blessed by children.

Other cake-related traditions include sending a boxed morsel of cake to all the guests/relatives who could not attend, and saving the top layer for the birth or christening/baptising of the first-born child.

Wedding cakes around the world
Many countries have very different ideas to the traditional fruit or sponge cake. A comprehensive list can be found at: https://www.theknot.com/content/a-world-tour-of-wedding-cake-traditions
Here are a couple of the more unusual ones:

Japan: Many Japanese use impostor cakes at wedding receptions. Made of artificial rubber or Styrofoam, these faux confections are iced with wax -- and even feature a slot for the bride and groom to insert a knife. While the impostors pose for photos, the real (less elaborate) cakes are cut in the kitchen and served to guests.

Greece: These days, most Greek couples prefer a flourless almond cake, filled with vanilla custard and fruit, and covered in sliced almonds. The traditional Greek wedding cake consists of honey, sesame seed, and quince, which is said to symbolize the couple's enduring commitment to each other. Sourdough wedding bread decorated with beads and blossoms is also a traditional treat.

Norway: Shying away from cake altogether, Norwegians serve brudlaupskling, a type of wedding bread first developed when white flour was a rarity on farms in Norway. Any food containing wheat was once highly prized, so the wedding bread was considered a true treat. Topped with cheese, cream, and syrup, this unique bread is folded over and cut into small squares and served to all the guests.

Lithuania: For many Lithuanians, the wedding cake is actually a cookie-like pastry shaped into a Christmas tree. Baked to a sunny yellow hue, the pastry, called a sakotis, is usually decorated with fresh flowers and herbs protruding from the top peak.

Indonesia: The cake traditionally served at Indonesia weddings is a massive, multilayered creation known as kek lapis. Typically made from layers of chocolate and vanilla, it dates back to the Dutch colonial period. Today's versions are often spiced with cinnamon and nutmeg