Raphael, Leo X and Cardinals, 1518 (Uffizi Gallery, Florence). Not interested in debating Martin Luther, Pope Leo X called him a heretic and sent him a papal bull of excommunication. Holy Roman Emperor Charles V stepped in to arbitrate, calling an Imperial Diet (or congress) at the town of Worms. Disgusted by this Diet of Worms, Luther refused to swallow his beliefs. "Here I stand," he told the assembly. "Unless you can convince me by scripture or by clear reasoning, I am bound by my beliefs...I cannot and I will not recant. God help me. Amen."