and soldiers and rowers levied, including over 20,000 manumitted slaves. Finally, Octavian and Agrippa defeated Sextus in the Battle of Naulochus in 36 BC, putting an end to all Pompeian resistance. Octavian's power was further enhanced after his victory against the combined fleets of Mark Antony and Cleopatra, Queen of Egypt, in the Battle of Actium in 31 BC, where Antony had assembled 500 ships against Octavian's 400 ships. This last naval battle of the Roman Republic definitively established Octavian as the sole ruler over Rome and the Mediterranean world. In the aftermath of his victory, he formalized the Fleet's structure, establishing several key harbors in the Mediterranean (see below). The now fully professional navy had its main duties consist of protecting against piracy, escorting troops and patrolling the river frontiers of Europe. It remained however engaged in active warfare in the periphery of the Empire. Principate Operations under Augustus Under Augustus and after the conquest of Egypt there were increasing demands from the Roman economy to extend the trade lanes to India. The Arabian control of all sea routes to India was an obstacle. One of the first naval operations under princeps Augustus was therefore the preparation for a campaign on the Arabian Peninsula. Aelius Gallus, the prefect of Egypt ordered the construction of 130 transports and subsequently carried 10,000 soldiers to Arabia. But the following march through the desert towards Yemen failed and the plans for control of the Arabian peninsula had to be abandoned. At the other end of the Empire, in Germania, the navy played an important role in the supply and transport of the legions. In 15 BC an independent fleet was installed at the Lake Constance. Later, the generals Drusus and Tiberius used the Navy extensively, when they tried to extend the Roman frontier to the Elbe. In 12 BC Drusus ordered the construction of a fleet of 1,000 ships and sailed them along the Rhine into the North Sea. The Frisii and Chauci had nothing to oppose the superior numbers, tactics and technology of the Romans. When these entered the river mouths of Weser and Ems, the local tribes had to surrender. In 5 BC the Roman knowledge concerning the North and Baltic Sea was fairly extended during a campaign by Tiberius, reaching as far as the Elbe: Plinius describes how Roman naval formations came past Heligoland and set sail to the north-eastern