Portsmouth Harbour is a natural harbour that has been used since at least Roman times. Indeed, the Romans built Portchester Castle to help defend it, and the coast, from Saxon raiders, on its northern shore. Flanked by Gosport on the west and Portsea Island to the east, Portsmouth Harbour became a major naval base and was heavily fortified. It is still the home of the Royal Navy, Her Majesty's Naval Base, Portsmouth, as well as now being a busy commercial ferry and freight port. A boat tour of the harbour takes in views of whichever ships happen to be in port at the time, as well as of historic buildings. A variety of tours are available, but one of the most popular runs from pier near HMS Warrior in Portsmouth Dockyard and is included in the ticket price for all attractions. Pictured is the aircraft carrier, HMS Queen Elizabeth.