It is by no means certain that in the first four centuries the city extended much further north than Cornhill, or further west than Dowgate, or to the east beyond the Tower, which from very early times had been a sort of fortress or citadel to protect the city on its south-eastern angle, although it did not develop into what we now call the Tower until long after.
The subsequent extension of the city both northward and westward may have taken place during the Roman occupation, but, if so, quite at the last; it is much more probable that it was during the Saxon period, perhaps even as late as Alfred's reign. In those early times the site now covered by St. Paul's was certainly not included within the walls.
From the river the Roman city could never have possessed the picturesque appearance which it assumed in later days, especially in mediaeval times.
The walls would have been of stone, bonded every four feet by three courses of red tile or Roman brick, each sixteen by twelve inches and one inch and a half thick. The stone used was that called Kentish Rag, which could easily be brought by barges up the river from Maidstone.
The bastions were similar, and were probably carried up higher than the wall, so as to allow for a chamber, or watching loft, with loophole windows. The thickness of the wall, which was eight feet, allowed for a covered way nearly at the top, and connecting bastion with bastion.
The foundation of this river wall was on oaken piles driven into the earth, on which a mass of chalk rubble was placed.
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