Final answer:
European rulers maintained their power in the era 600-1300 by controlling the religious institutions.
Step-by-step explanation:
One specific way European rulers maintained their power in the era 600-1300 was by controlling the religious institutions. The Catholic Church played a significant role during this time, and rulers often allied themselves with the Church to gain legitimacy and authority. By having control over the religious institutions, rulers could influence the beliefs and behaviors of the people, which helped maintain their power.