The Gurjara-Pratiharas were instrumental in containing Arab armies moving east of the Indus River. Nagabhata I defeated the Arab army under Junaid and Tamin during the Caliphate campaigns in India. Under Nagabhata II, the Gurjara-Pratiharas became the most powerful dynasty in northern India. He was succeeded by his son Ramabhadra, who ruled briefly before being succeeded by his son, Mihira Bhoja. Under Bhoja and his successor Mahendrapala I, the Pratihara Empire reached its peak of prosperity and power. By the time of Mahendrapala, the extent of its territory rivalled that of the Gupta Empire stretching from the border of Sindh in the west to Bengal in the east and from the Himalayas in the north to areas past the Narmada in the south. The expansion triggered a tripartite power struggle with the Rashtrakuta and Pala empires for control of the Indian subcontinent. During this period, Imperial Pratihara took the title of Maharajadhiraja of Āryāvarta (Great King of Kings of India).