power the partisans of secular authority had only a half-hearted
doctrine to oppose. Ever since the days of Pope Gelasius I (492-6),
the Church herself had accepted the view of a strict dualism in the
organisation of society and, therefore, of the theoretical equality
between the ecclesiastical and the secular organs of government.
According to this doctrine Sacerdotium and Imperium are independent
spheres, each wielding the one of the two swords appropriate to
itself, and thus the Emperor no less than the Pope is _Vicarius
Dei_. It is this doctrine behind which the champions of the Empire
entrench themselves in their contest with the Papacy. It was asserted
by the Emperors themselves, notably by Frederick I and Frederick II,
and it has been enshrined in the writings of Dante.

[Sidenote: Its weakness.]

The weak point of this theory was that it was rather a thesis for
academic debate than a rallying cry for the field of battle. Popular
contests are for victory, not for delimitation of territory. And its
weakness was apparent in this, that while the thorough-going partisans
of the Church allowed to the Emperor practically no power except such
as he obtained by concession of or delegation from the Church, the
imperial theory granted to the ecclesiastical representative at least
an authority and independence equal to those claimed for itself, and
readily admitted that of the two powers the Church could claim the
greater respect as being entrusted with the conduct of matters that
were of more permanent importance.

Moreover, historical facts contradicted this idea of equality of
powers. The Church through her representatives often interfered with
decisive effect in the election and the rejection of secular