Why an Engagement Ring?

The custom of giving an engagement ring as a symbol of a man’s commitment to his future wife supposedly originated from the Romans. The prospective husband gave his bride-to-be a ring which acted as a symbol of the cycle of life and eternity. This was performed at a formal ceremony.

Again, the Wikipedia gives some great further reading on this if you are interested:

http://en.wikipedia.org/wiki/Engagement_ring