At what period a fortress was first built on the spot now occupied by the Tower will probably never be known, though it must have been a place of some strength when Edmund Ironside defended it against the Danes, and probably was centuries before that period. No one doubts but that London was long inhabited by the Romans; and from all we know of the many habits of those cautious warriors, we are certain that they would not leave the river front of their city undefended. Ancient foundations have been discovered in the Tower within the last century, so strong and thick, as to call back Fitz-Stephen's description of those large and strong walls which rose up from a deep foundation, the mortar of which is "tempered with the blood of beasts." Nearly seven hundred years ago did Fitz-Stephen write thus; so that the "Tower Palatine," as he calls it, must have been so ancient even in his day, that he knew nothing of its origin, more than that of the mortar being "tempered with the blood of beasts." Nearly all our Roman remains in Lower Thames-street have been discovered "deep down," and this goes far in favour of those strong and undated foundations, laid bare within the Tower, being Roman; the great width--three yards--corresponds also with all we have seen of such ancient relics. We know that the first London Bridge was built of wood, but we know not the date of its erection, though it is mentioned many times long before the Norman invasion. We also know that Edmund Ironside defended a walled fortress which stood on the City side of the river; and that in those days there was a bridge which Canute the Dane's ships did not pass under, and that the battle on the river and on land was at the foot of this old wooden bridge; and that the wall Edmund and his followers defended must have been somewhere about the spot on which the Tower now stands. This battle took place more than eight hundred years ago; and after Canute's forces were repulsed by the London citizens, headed by the son of Ethelred the Unready, the Danish king sailed out of the Thames and landed in Mercia, somewhere near the mouth of the Humber. This fortress was defended, and this wooden bridge stood, more than 150 years before Peter of Colechurch commenced his stone bridge in 1176; but how much longer we know not. London must have been well fortified to have held out as it did, against the invasion of Swein king of Denmark, who came up to its very walls with his ships, and was compelled to retreat. There must have been either tower or fortress beside the river, for the Saxon citizens to have driven back such a powerful enemy.