 A Vedic Yuga had 1,860 "tithis" (, dates), and it defined a "savana"-day (civil day) from one sunrise to another.The Rigvedic version of Jyotisha may be a later insertion into the Veda, states David Pingree, possibly between 513 and 326 BCE, when Indus valley was occupied by the Achaemenid from Mesopotamia.The mathematics and devices for time keeping mentioned in these ancient Sanskrit texts, proposes Pingree, such as the water clock may also have arrived in India from Mesopotamia.