The period between AD 320–550 is known as the Classical Age, when most of North India was reunited under the Gupta Empire (c. AD 320–550). This was a period of relative peace, law and order, and extensive achievements in religion, education, mathematics, arts, Sanskrit literature and drama. Grammar, composition, logic, metaphysics, mathematics, medicine, and astronomy became increasingly specialized and reached an advanced level. The Gupta Empire was weakened and ultimately ruined by the raids of Hunas (a branch of the Hephthalites emanating from Central Asia). Under Harsha (r. 606–47), North India was reunited briefly.