Ravana’s greatest strength

Ravana’s greatest strength lies in his divine armor of Brahma and his extraordinary regenerative powers. Together, these made him virtually invincible even the gods, including Vishnu, could not bring him down. The Ramayana mentions that Vishnu hurled his Sudarshana Chakra at Ravana countless times, yet it could only inflict minor wounds, which were either absorbed by his armor or quickly healed by his regeneration. He was struck hundreds of times during the wars with gods with the blows of Vishnu’s discus as also with the strokes of other weapons in great conflicts. However, Ravana chose to keep certain marks as trophies of his battles such as the wound from Airavata, the scars left by Vishnu’s disc, and those from Indra’s Vajra. Indra possessed the unique arrow crafted by Brahma, the only weapon capable of piercing Ravana’s armor and destroying his heart, instantly killing him and preventing any chance for regeneration. However he did not used it upon Ravana as it would violate Brahma's boon to him. In the final battle between Rama and Ravana, the latter's armor and regenerative powers made it nearly impossible to defeat him. The only way to end his life was to strike his heart the source of his life in a single blow. For this, Rama employed the unique arrow gifted to him by Sage Agastya, which had originally been given to Agastya by Indra. Vishnu' even if he possessed this arrow cannot use it as Brahma's boon would be violated in such a situation. But Ram had no such constraints. Although in human form he needed additional power like blessings of Sun god through aditya Hrdaya stotra, Bala - Atibala vidya which Vishwamitra imparted and most importantly this arrow which Agastya gave him foreseeing these events.