When did the practice of wearing wedding rings become popular? Why is the ring worn on the third finger (not counting the thumb) of the left hand?

Some believe the practice is a vestige of ancient barbarian marriages - when a man would capture a woman and bind her to his house in fetters, now symbolized by a ring. Others think the practice originated in ancient Egypt about 2800 B.C. As the circular ring has no beginning or end, it is the perfect symbol of the eternal bond of marriage.

The custom of wearing the wedding ring on the third finger of the left hand began with the Greeks in the third century B.C. Greek physicians believed that this finger contained a "vein of love" that ran directly to the heart. (The Book of Answers, by Barbara Berliner)