The word diamond comes from the Greek word adamas which means invincible or indestructable. Because of a diamond's incredible hardness it has been forever linked with that meaning. It is believed a rough diamond was fastened unto the breastplate of warrior kings to protect them. It is also the genesis of the tagline "A Diamond Is Forever."
The first cutting centers may have started as early as the mid 1300's. The first recorded diamond engagement ring was given in 1477 when Archduke Maximillian presented one to his betrothed, Mary of Burgundy. Prior to that, engagement rings featured more common gemstones, or were simple metal bands. It wasn't until after 1870 that there were enough diamonds mined to satisfy demand that they became the dominant engagement ring stone.
Ultimately it is the diamond's light handling ability as well as its hardness that has made it the most sought after gemstone in the world. A finely cut diamond is truly a marvel of art, mathematics and nature combined.