About 1053 Constantine IX disbanded what the 11th century Greek historian John Skylitzes calls the "Iberian Army", which consisted of 50,000 men. Skylitzes' contemporaries, the former officials Michael Attaleiates and Kekaumenos, agree that by demobilizing these soldiers Constantine did catastrophic harm to the Empire's eastern defenses. Constantine made a truce with the Seljuks that lasted until 1064, but a large Seljuk army under Alp Arslan attacked the theme of Iberia and took Ani; after a siege of 25 days, they captured the city and slaughtered its population.