 One factor that unites the different strands of Hinduism is the importance of foundational texts composed between ca. 1600 and 700 BCE. These include the Vedas, which contain hymns and prescriptions for performing rituals, Brāhmaṇa, accompanying liturgical texts, and Upaniṣad, metaphysical treatises. The Vedas discuss gods who personify and embody natural phenomena such as fire (Agni) and wind (Vāyu). More gods appear in the following centuries (e.g., Gaṇeśa and Sati-Parvati in the 4th century). Note that there are both polytheistic and monotheistic strands in Hinduism, so it is not the case that individual believers worship or recognize all of these gods. Ancient Vedic rituals encouraged knowledge of diverse sciences, including astronomy, linguistics, and mathematics. Astronomical knowledge was required to determine the timing of rituals and the construction of sacrificial altars. Linguistics developed out of a need to formalize grammatical rules for classical Sanskrit, which was used in rituals. Large public offerings also required the construction of elaborate altars, which posed geometrical problems and thus led to advances in geometry. Classic Vedic texts also frequently used very large numbers, for instance, to denote the age of humanity and the Earth, which required a system to represent numbers parsimoniously, giving rise to a 10-base positional system and a symbolic representation for zero as a placeholder, which would later be imported in other mathematical traditions (Joseph 1991 [2000]). In this way, ancient Indian dharma encouraged the emergence of the sciences.