The custom of celebrating birthdays is very old. Ancient people did not have calendars. They kept track of time using the sun and moon. They marked the season a child was born. The birthday was celebrated sometime during the same season each year. Many of the customs we use to celebrate birthdays began hundreds of years ago.
The custom of baking a birthday cake has many origins. Cakes have been made for centuries as offerings to various gods. Cakes were sometimes offered to the gods for good luck. Some say the custom of cake offerings began in Germany. The round cake was made in association with the celebration of the birth of Christ. Birthday cakes are probably the most important symbol associated with a birthday celebration.
Another symbol tied to the birthday cake is the custom of putting candles on the cake.