Boulogne, Carausius had deprived his master of
the means of pursuit and revenge. And when, after a vast expense of time
and labor, a new armament was launched into the water, [29] the Imperial
troops, unaccustomed to that element, were easily baffled and defeated
by the veteran sailors of the usurper. This disappointed effort was
soon productive of a treaty of peace. Diocletian and his colleague, who
justly dreaded the enterprising spirit of Carausius, resigned to him
the sovereignty of Britain, and reluctantly admitted their perfidious
servant to a participation of the Imperial honors. [30] But the adoption
of the two Caesars restored new vigor to the Romans arms; and while
the Rhine was guarded by the presence of Maximian, his brave associate
Constantius assumed the conduct of the British war. His first enterprise
was against the important place of Boulogne. A stupendous mole, raised
across the entrance of the harbor, intercepted all hopes of relief. The
town surrendered after an obstinate defence; and a considerable part of
the naval strength of Carausius fell into the hands of the besiegers.
During the three years which Constantius employed in preparing a fleet
adequate to the conquest of Britain, he secured the coast of Gaul,
invaded the country of the Franks, and deprived the usurper of the
assistance of those powerful allies.

[Footnote 29: When Mamertinus pronounced his first panegyric, the naval
preparations of Maximian were completed; and the orator presaged an
assured victory. His silence in the second panegyric might alone inform
us that the expedition had not succeeded.]

[Footnote 30: Aurelius Victor, Eutropius, and the medals, (Pax Augg.)
inform us of this temporary reconciliation; though I will not presume
(as Dr. Stukely has done, Medallic History of Carausius, p. 86, &c) to
insert the identical articles of the treaty.]

Before the preparations were finished, Constantius received the
intelligence of the tyrant's death, and it was considered as a sure
presage of the approaching victory. The servants of Carausius imitated
the example of treason which he had given. He was murdered by his first
minister, Allectus, and the assassin succeeded to his power and to his
danger. But he possessed not equal abilities either to exercise the one
or to repel the other.

He beheld, with anxious terror, the opposite shores of the continent
already filled with arms, with troops, and with vessels; for Constantius
had