Sub Umbras, meaning 'Under the Shadows,' reflects the themes of concealment, protection, and the interplay of fate and free will in Vergil's Aeneid. This concept is vital in illustrating how characters navigate their desires and decisions while influenced by larger, often dark forces beyond their control. In Book 4, Lines 659-705, it emphasizes the emotional turmoil faced by Dido as she grapples with her love for Aeneas against the looming shadow of fate that dictates his departure.