In many cultures, the circle was considered to be the symbol of perfection, unity, and eternity. This gives us the basic symbolism of a ring that makes it especially suited to pledging one's love.

However, the earliest engagement rings were pure business. They doubled as wedding rings, serving to seal the act of sale which transferred ownership of a daughter from father to husband (hence the practice of giving away the bride). Such rings were usually of solid gold to prove the groom's worth.

The Romans supposedly believed that the third finger of the left hand had a special vein that ran directly to the heart. While having no basis in scientific anatomy, the romantic custom still stands. King Edward VI of England designated the third finger, left hand, as the official "ring finger" and in 1549 the Book of Common Prayer designated the left hand as the marriage hand.

The current archetypal engagement ring is the round Tiffany-cut diamond solitaire on a gold band. The actual Tiffany's 2000 model is square-cut--quite nifty.

Colored gemstone engagement rings are currently uncommon, although they are traditional among the royal families of Europe. However, the idea is regaining popularity. Non-traditional rings that don't necessarily cost a fortune are also becoming popular. Poesy rings, silver rings, and so on are still romantic and pretty, but also more original and meaningful. Rings inspired by various cultures and traditions, such as Claddagh rings or solid jade bands, are also a new trend for the nonconformist. And there is even the occasional engagement pendant or other non-ring piece. The two-months' salary price benchmark is believed to have been invented by De Beers to get people to spend excessively, when it's really the love that counts.