The Palas were astute diplomats and military conquerors. Their army was noted for its vast war elephant corps. Their navy performed both mercantile and defensive roles in the Bay of Bengal. They built grand temples and monasteries, including the Somapura Mahavihara, and patronised the great universities of Nalanda and Vikramashila. The Proto-Bengali language developed under Pala rule. The empire enjoyed relations with the Srivijaya Empire, the Tibetan Empire and the Arab Abbasid Caliphate. Abbasid coinage found in Pala archaeological sites, as well as records of Arab historians, point to flourishing mercantile and intellectual contacts. The House of Wisdom in Baghdad absorbed the mathematical and astronomical achievements of Indian civilisation during this period.