The 7th and 6th centuries BC witnessed the composition of the earliest Upanishads. Upanishads form the theoretical basis of classical Hinduism and are known as Vedanta (conclusion of the Vedas). The older Upanishads launched attacks of increasing intensity on the ritual. Anyone who worships a divinity other than the Self is called a domestic animal of the gods in the Brihadaranyaka Upanishad. The Mundaka launches the most scathing attack on the ritual by comparing those who value sacrifice with an unsafe boat that is endlessly overtaken by old age and death.