Five hundred men laboured incessantly at the work. The stone for the walls was fortunately found close at hand, but, notwithstanding this, the work took nearly six months to execute; deep wells were sunk in the centre of the fort, and by this means an ample supply of water was secured, however large might be the number within it.

A very short time after the commencement of the work the news arrived that King Edmund of East Anglia had gathered his forces together and had met the Danes in a great battle near Thetford on Sunday the 20th of November, and had been totally defeated by them, Edmund himself having been taken prisoner. The captive king, after having been for a long time cruelly tortured by the Danes, was shot to death with arrows. It was not long after this that news came that the whole of East Anglia had fallen into the hands of the Danes.

Early in the month of February, 871, just as the walls of his fort had begun to rise, a messenger arrived from the king bidding Edmund assemble all the men in his earlship and march at once to join him near Devizes, as the news had come that a great Danish fleet had sailed up the Thames and had already captured the royal town of Reading.