The word is also found in ancient post-Vedic Sanskrit texts such as in section 2.451 of the "Mahabharata" and section 4.27.16 of the "Ramayana". These usages are in different contexts. For example, "Durg" is the name of an Asura who had become invincible to gods, and "Durga" is the goddess who intervenes and slays him. "Durga" and its derivatives are found in sections 4.1.99 and 6.3.63 of the "Ashtadhyayi" by Pāṇini, the ancient Sanskrit grammarian, and in the commentary of Nirukta by Yaska. "Durga" as a demon-slaying goddess was likely well established by the time the classic Hindu text called "Devi Mahatmya" was composed, which scholars variously estimate to between 400 and 600 CE. The "Devi Mahatmya" and other mythologies describe the nature of demonic forces symbolised by Mahishasura as shape-shifting and adapting in nature, form and strategy to create difficulties and achieve their evil ends, while Durga calmly understands and counters the evil in order to achieve her solemn goals.