It must be premised that the course of the Thames, the containing bounds, the depth of the stream, the character of the rivulets--such as the Lea, the Fleet, Wall-brook, West-Bourne, Tye-Bourne--presented marked differences in early historic days from the appearance they show to-day. The sites north and south of the line where London Bridge now stands constituted firm ground, with a tendency to an elevation in the north. These facts determined the position of the British settlement. At that part of the river the Britons had, if not a ford, at least a ferry, and finally a rough bridge--perhaps of coracles or boats--the progenitor of the noble structure now existing. The ferry went from what is now Dowgate to a similar opening still existing to the west of St. Saviour's, Southwark. A British settlement of an early date would not now be thought to deserve the name of town. No less an authority than Julius Caesar tells us that it was nothing more than a thick wood, fortified with a ditch and rampart, to serve as a place of retreat from the inroads of enemies. At that time, we may, therefore, imagine a clearing carved out of the forest, extending probably from the site of St. Paul's Cathedral to that of the Bank of England, the dwellings of the Britons being spread about the higher ground looking down upon the river, including Tower Hill. At the time of the revolt of the Iceni, the Roman governor, Paulinus Suetonius, being unable to make a stand, abandoned London to Boadicea, who entirely destroyed the city, after having massacred the inhabitants. We find London holding an important place in the Antonine Itinerary, Londinium being a starting point for nearly half the routes described in the portion devoted to Britain. Traditionally, Constantine the Great walled the city, at the request of his mother Helena, who is said to have been a native of Britain. Probably we should place the northern wall somewhere along the course of Cornhill[5] and Leadenhall Street; the eastern in the direction of Billiter Street and Mark Lane; the southern in the line of Upper and Lower Thames Streets; the western on the S.W. side of Walbrook. About the centre of each side might be placed the four main gates, corresponding with Bridge Gate, Ludgate, Bishopsgate and Aldgate. [Footnote 5: Perhaps somewhat to the north of the modern street. A portion is to be seen in the churchyard of St. Giles, Cripplegate.]