The city of Ostia was founded circa 340 BC. Located at the mouth of the Tiber river, approximately 36 km from the center of Rome, Ostia was in a very strategic position to link the Capital of the Roman
Empire with the rest of the world by sea. Even if the spectacular remains of the city are now located inland, Ostia was, at the empire time, right on the sea. 
At the time, what was the world’s largest port was used as a Naval base as well as a commercial maritime naval platform capable of hosting over 600 ships at the same time.
Rome not having a port matching with the “grandeur” of the empire could not be accepted by the emperors. 
According to Seneque, after Caligula passed away, Rome that was already over a million people and had only a week left of provisions.
Thus, in 42 AC, Emperor Claudius who had just gained power, started works on Port Claudius. It took 20 years for Rome to have a port capable of supporting the new Emperor's ambitions.
Despite the gigantism of the project and the negative opinions from the empire’s leading engineers and architects, Claudius gave the order to start construction on a site 4 km away from Ostia.
The Roman engineeners used a laguna to create an artificial basin of 90 hectares that was digged between 4 and 5 meter depth.
The entry to the port was protected by a man made 758 meter long by 30 meter wide jetee of which one side was linked to the land.
Vessels were entering the port through a 206 meter chanel.
Experts estimate that the excavation of Portus Claudius needed 30.000 slaves for a period of almost 20 years.
They started works under the reign of Claudius in year 42 but they were achieved under Néron, approximately in 64 or 66. 
Roman money dating back from this era shows an image of Portus Claudius.
The port was attached to the Port of Trajan approximately 50 years later.
This exhagonal shaped artificial port was digged inside the land and each side of the exhagon is 360 meter long.
It's location was offering total safeheaven during the worst storms. More than 2,000 meter of concrete and stone docks are still visible on its six sides.
This huge infrastructure was inaugurated by Emperor Nero in A.D. 64.
Its main purpose was to ensure the safe loading and unloading of goods from the large cargo vessels arriving from across the Mediterranean, and the transfer of commodities onto smaller boats (Naves Caudicariae) that sailed up the river to the center of Rome.
The port basin was partially excavated inland and partially projected into the sea, with two large piers converging to the port entrance to the west.
Here, on an artificial island, a lighthouse similar to the famous Alexandria's guided the ships to the port entrance.