This may be understood of any harbour; but it is generally interpreted
to refer to the _Portus Julius_, a haven formed by letting in the sea
upon the _Lucrine Lake_, and forming a junction between that and the
Lake _Avernus_; a work, commenced by Julius Caesar, and compleated by
Augustus, or Agrippa under his auspices. _Regis opus!_ Both these
lakes (says Martin) were in Campania: the former was destroyed by an
earthquake; but the latter is the present _Lago d'Averno_. Strabo, the
Geographer, who, as well as our Poet, was living at the time, ascribes
this work to Agrippa, and tells us that the Lucrine bay was separated
from the Tyrrhene sea by a mound, said to have been first made by
Hercules, and restored by Agrippa. Philargyrius says that a storm arose
at the time of the execution of this great work, to which Virgil seems
to refer in his mention of this Port, in the course of his Panegyrick on
Italy in the second Georgick.
An memorem portus Lucrinoque addita claustra,
Atque indignatem magnis strideribus aequor,
Julia qua ponto longe sonat unda refuso,
Tyrrbenusque fretis immittitur aeflut AVERNIS?
Or shall I praise thy Ports, or mention make
Of the vast mound, that binds the Lucrine Lake?
Or the disdainful sea, that, shut from thence,
Roars round the structure, and invades the fence;
There, where secure the Julian waters glide,
Or where Avernus' jaws admit the Tyrrhene tide?
DRYDEN.