 Previously chariots ("Ratha") were used in warfare, but in medieval times chariots were replaced by camels ("Oṣṭra").So, the bishop in olden days was called "Ratha" / "Śakaṭa" and in medieval ages was called "Oṣṭra".This name may be derived from the Sanskrit word "Chaturanga" or Persian word "Chatrang".