The underworld in Roman mythology plays a crucial role as the realm of the afterlife. Known as Hades, it is where souls go upon death, influenced by their deeds in life. The concept is divided into different areas such as Fields of Elysium for the virtuous and Tartarus for the wicked, reflecting the moral judgments imposed on souls. It serves as both a place of reward and punishment, reinforcing the Roman ideals of virtue and justice after death.