The Middle Ages
Around the year 850, Pope Nicholas I formalized the notion of engagement, stating that an engagement ring symbolized the intention to marry. Given only by the man to his future wife, it represented a financial sacrifice, and was most often made of gold.
In the Middle Ages, engagement rings were adorned with sapphires and rubies, but this was not yet a widespread practice. The fashion for stone-set engagement rings came, like many fashions, from a powerful man. The Archduke Maximilian of Austria was the originator, with the diamond-set ring he gave to Marie de Bourgogne. A far cry from the solitaire so popular today, the ring was set with diamonds representing the letter "M".
According to the GIA (Gemmological Institute of America), stone-cutting techniques of the time made them appear dull, almost black. It was only the diamond's high resistance to fire and steel that made it a desirable stone, symbolizing durability. To compensate for the low brilliance of the stones, jewelers created ornamental settings, with rose and fleur-de-lys motifs for example.