Complex sentence: A possible explanation is that Vergil left it in the care of Veterani, who inscribed the colophon to associate it with his other treasures so that it would not be lost or damaged during the Papal invasion in Urbino in 1516.
Split into simpler sentences: A possible explanation for Veterani's note is that Vergil left it in Veterani's care, who inscribed the colophon to associate it with Veterani's other treasures. This way, it would not be lost or damaged during the Papal invasion in Urbino in 1516.