The walls of the original 12th century gatehouse slightly subsided on the western side, rendering the inner portcullis unusable.   Therefore King John rebuilt the gatehouse, adding two D-shaped towers to the South.

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         The arrow slit on the south wall is too low, confirming that the level of the Tiltyard must have been later raised substantially.   The large ground floor opening in the West chamber was likely to have been for a sally port, before becoming flooded by the accompanying rise in the level of the mere, and then being repurposed as a latrine, as it is now typically described.

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         According to historian Sir William Dugdale, the Mortimer family crest was engraved above the entrance, and so Mortimer’s was the name Dugdale used for this tower.   The crest could have been that of either Roger Mortimer, earl of March, who hosted the martial tilting event attended by 100 knights in 1279, or Sir John Mortimer, who was later detained here by Henry V.

  

          To the West of this tower a culvert brought water from the mere into the inner court, to power a mill before then turning to exit under the Water Tower.