Tapas to Brahma

Following his initial training, Ravana performed an intense penance to Brahma (the Creator God), lasting several years. He chopped his head for 10 times in an anger towards brahma not appearing for his penance, each time when he sliced his head new head will arise and thus continued his penance. Atlast Brahama pleased with his austerity appeared after he slewed his head for 10th time and offered him a boon. Ravana asked for immortality, which Brahma refused to give, but gave him the celestial nectar of immortality. The nectar of immortality, which was stored under his navel, according to which he could never be vanquished till the nectar was dried out.Ravana then asked for absolute invulnerability and supremacy before gods and heavenly spirits, other demons, serpents, and wild beasts. Contemptuous of mortal men, he did not ask for protection from these. Brahma granted him these boons, and additionally his 10 heads that he severed, along with great strength by way of knowledge of divine weapons and sorcery. Thus ravana known to be 'Dasamuga' (Dasa = ten, muga = face).