Following the death of Pope Adrian IV, Rolando of Siena was elected pope as Alexander III on 7 September 1159. His election immediately plunged the Church into schism: on the same day, Cardinal Ottaviano de' Monticelli was proclaimed antipope Victor IV. Each excommunicated the other, but Victor’s authority was confined largely to territories controlled by the Holy Roman Emperor Frederick I, whose support transformed the schism into a prolonged contest between papal independence and imperial power.

Alexander III’s resistance to Frederick I defined his pontificate. Forced into exile for much of the 1160s, he nevertheless secured recognition from France, England, and much of Western Christendom, while condemning imperial interference in papal elections. The struggle culminated in Frederick’s defeat by the Lombard League and the Peace of Venice (1177), in which the emperor formally recognised Alexander as the legitimate pope.

At the same time, Alexander III played a decisive role in the conflict between Henry II and Thomas Becket ⓘ, Archbishop of Canterbury. Supporting Becket’s defence of ecclesiastical rights against royal control, Alexander acted cautiously—balancing moral authority with political necessity—yet consistently upheld Becket’s position. Following Becket’s murder in Canterbury Cathedral in 1170, Alexander canonised him in 1173, turning the archbishop into a powerful symbol of resistance to royal overreach.

Through these intertwined struggles, Alexander III emerged as a central architect of the later medieval papacy: affirming papal legitimacy against imperial power, defending clerical autonomy against kings, and shaping the Church’s political authority across Europe.