Why were Francis I’s two eldest sons held as hostages in Spain?

Francis I’s two eldest sons were held as hostages in Spain as a mandatory condition of the Treaty of Madrid, signed in January 1526.1

Following his capture by the Holy Roman Emperor Charles V at the Battle of Pavia in 1525, Francis I was imprisoned in Madrid. To secure his release, the King was forced to agree to harsh terms, which included the delivery of his two eldest sons—the seven- and eight-year-old princes—to serve as hostages.231

The Emperor held the children captive for four years as a guarantee of the treaty's execution. They were eventually released in 1530 following the Treaty of Cambrai, a revised agreement negotiated by the King's mother that required Francis to pay a significant ransom and abandon his claims in Italy.14