The relations between sacerdotium and imperiurn in the Middle Ages went through alternate phases, and the two centres of power were sometimes enemiesand at other times of reciprocal aid and support.

Gregory VII's work was itself in part prepared for by events of the thirty years before his accession.

So, when in the eleventh century the Church of Rome passed through one of its darkest periods, the Emperor Henry III delivered the papacy from the hands of the local Roman families, as Defensor Ecclesiae, deposing straight away three popes (Synod of Sutri, 1046), Benedictus IX, Silvester III and Gregory VI, and instituted a succession of German popes (starting with the bishop Suigerius of Bamberg who took the name of Clement II), who between 1046 and 1057 began to exercise more firmly the authority of the Church.

Leo IX (1048-54), in particular, took a strong lead in seeking to extirpate the moral abuses which contemporary reformers so vociferously condemned.

From 1059 Hildebrand, the future Gregory VII, stood near to the centre of affairs as archdeacon of the Roman Church; and it was with him that there took shape that reform of the Church already begun in Cluniac circles. When he became pope he sought with an altogether new resolution and zeal to bring to fruition the work which his predecessors had initiated. Simony and clerical marriage quickly became and always remained the objects of his energetic action. But he also sought wider ends which had been foreshadowed but not clearly articulated before, that is, to secure the reform of the Church, to achieve what he and his supporters called its 'liberty'.

This cardinal concept of the Gregorian reform meant the freeing of the Church from every kind of subordination, and the exclusive lordship of St Peter as prince of the apostles and as recipient of Christ's commission to feed his sheep.

This led to the ‘Investiture Contest’ with the Emperor Henry IV, and the conflict brought the excommunication of the Emperor and led to the famous meeting in Canossa (28 January 1077).

The Emperor then occupied Rome in 1083, enthroning an antipope, Guibertus of Ravenna (Clement III), who crowned him in Campidoglio (31 March 1084); the Roman Curia with almost all the Cardinals took sides with the winner of that moment, and Gregory VII was forced to flee.