In medieval Europe, hostages were given, not taken. They were a means of guarantee used to secure transactions ranging from treaties to wartime commitments to financial transactions.
The word itself has caused debate among etymologists. Some sources think it is related to the Latin hostis, "stranger." It seems more likely it is from Old French ostage, which was used for both pledge or bail and kindness or hospitality. In turn this was from Latin obsidanus, meaning literally "to sit before" and meaning people who were hostages.
A hostage was a pledge of financial payment or cooperation. One example was Philip of Courtenay. Another was William Marshal. William served five English kings, starting with Henry II. When he was a boy, his father, John, opposed King Stephen in favor of the Empress Matilda (this was during "The Anarchy"). Stephen was besieging John's Newbury Castle, and John promised he would eventually surrender the castle and offered William as hostage/surety for his promise.
John used the time it bought him, however, to reinforce the castle and send word to Matilda's forces of what was happening. Stephen found out, and ordered John to surrender immediately, or else William would be hanged. John called Stephen's bluff, saying "I still have the hammer and the anvil with which to forge still more and better sons!" Stephen started to arrange to have William catapulted at the castle, but could not do it. Harming a hostage and harming a child were not easily done.William was released only after several months went by and a peace treaty was signed to end the war.
Another famous hostage was King John of France (26 April 1319 – 8 April 1364) during the Hundred Years War. The English under Edward, the Black Prince, dominated at the Battle of Poitiers, although the French army was probably twice the size. John was captured by a French exile who had sided with the English, Denis de Morbecque, who promised to lead John to the Prince of Wales. John surrendered by handing over his glove.
John was taken to England, where he lived in high style for years. He was allowed to travel the country, and had a budget that included buying pets and clothing and having his own court astrologer and a court band. He would be a hostage while a treaty (including ransom) favorable to the English would be negotiated.
His son, the Dauphin, had great difficulty arranging things back in France. The Estates General, a consulting and legislative body of the various estates in France, were angry over the mismanagement of resources (taxes and men) in a disastrous military engagement. They demanded political concessions in exchange for money, which the Dauphin refused. King John would remain a hostage, hosted by King Edward, for a total of four years. How he was able to go home, and why he then went back to England to place himself in captivity, will be explained tomorrow.