Troyes has been in existence since the Roman era, and through the centuries gained great importance as a medieval centre of commerce.
Louis the Stammerer in 878 received at Troyes the imperial crown from the hands of Pope John VIII. At the end of the ninth century, the counts of Champagne chose Troyes as their capital. In 1285, when Philip the Fair united Champagne to the royal domain, the town kept a number of privileges. John the Fearless, Duke of Burgundy and ally of the English, aimed in 1417 at making Troyes the capital of France, and he came to an understanding with Isabeau of Bavaria, wife of Charles VI of France, that a court, council, and parliament with comptroller's offices should be established at Troyes. It was at Troyes, then in the hands of the Burgundians, that on 21 May, 1420, the treaty was signed by which Henry V of England was betrothed to Catherine, daughter of Charles VI, and was to succeed him to the detriment of the dauphin. The dauphin, afterwards Charles VII, and Joan of Arc recovered the town of Troyes in 1429.
The 1420 Treaty of Troyes, which attempted to settle the Hundred Years' War, was signed here. During the Middle Ages, it was an important trading town, and gave its name to troy weight.