Euxine, and established naval stations on the great frontier rivers, the Euphrates, the Danube, and the Rhine.[e] [Illustration: ROMAN SHIP WITH SCALING LADDER, FOR ATTACKING A SEA WALL] It was only to be expected that the victor of Actium should not neglect the fleet, to which he owed everything, to the same extent as the republic had done; and as matter of fact he made a permanent navy the counterpart of his standing army. Up to that time Rome had only fitted out a fleet, or caused her allies to fit it out, for some definite purpose, and had dismissed it at the conclusion of the war. Augustus realised that a change must be made in this respect now that the whole coast of the Mediterranean was Roman and the sea had become the centre of the empire. His first care was to construct the requisite naval ports. The Adriatic coast of Italy is not rich in harbours, even leaving naval ports out of the question. Brundusium was too much of a trading mart to come into consideration as a possible naval station for the empire; while Ravenna, farther to the north, near the delta of the Po, appeared to answer the end the emperor had in view. The place was easy to defend on account of the marshes about it; the harbour, though none of the best, was capable of improvement; and by means of the imperial canal (Fossa Augusta) Augustus secured a communication between his new naval station and the southern mouth of the Po. This was an advantage as far as the provisioning of the forces was concerned, for the produce of the fertile basin of the Po could thus be shipped direct to Ravenna; on the other hand it probably accelerated the silting up of the harbour. The whole scheme seems to have been put in hand shortly after the battle of Actium, for we meet with what appears to be a reference to these works in the writings of Valgius Rufus in the first years of the empire. During the civil wars the fleet had used the Julian harbour on the west coast of Italy, but its inconvenient entrance and deficient anchorage unfitted it for a regular naval station. It was therefore abandoned in favour of the neighbouring harbour of Misenum, which surpassed even that of Ravenna in importance. From both stations small bodies of men used to be detached to Rome to protect the emperor and the capital. The marines naturally did not find much to do at Rome; when the emperor arranged a sea fight (naumachia) he counted, of course, upon their co-operation, at other times they were deputed to spread the awnings at the entertainments given to the people. Of less importance and probably of briefer duration was a similar work of Augustus on the coast of Gaul. Forum Julii (Fréjus) was raised by him to the rank of a naval station soon after the battle of Actium, and may have attained a certain degree of importance during the Cantabrian War; in the latter days of the empire we find no mention of any such naval port.