The tunnels which linked the spur redan and St. Johns tower to the northern entrance were originally constructed in the 13th century after the 1216 siege. The spur has undergone numerous periods of alteration and modernisation but the Medieval tunnels have remained throughout and provide the primary means of access to the spur from the castle.

The Medieval spur is likely to have been oval in shape (though there is considerable uncertainty about this) and the medieval tunnel towards the spur incorporated three passages which it is thought led to three towers, probably similar to St. Johns tower, the junction of these three truncated passages survives beneath the redan. Summarised from sources (1-2)

<1> English Heritage, 2014, Dover Castle Conservation Management Plan Volume 2 Gazetteer (Unpublished document). SKE52105.

<2> Johnathan Coad, 1995, English Heritage Book of Dover Castle and the Defences of Dover (Monograph). SKE52106.