A deer bank was a huge ditch and bank systems built in Medieval times by the owners of woods in order to prevent the passage of deer and cattle over the boundary. During the 12th and 13th centuries Norsey Wood was part of the Forest of Essex, which during these centuries was Royal Forest - the King's hunting ground, which was protected by Forest Law. Under Forest Law landowners could only hunt or take wood out of the forest with the King's permission. This was done by licence. Crondon Park during this same period belonged to the Bishop of London. Another name for a deer bank was a deer leap.

Whilst the deer bank that survives in Norsey Wood is of a later construction than the original one and was superimposed on the original one that which survives in Swan Wood is the original deer bank.

To the best of my knowledge from walking round Swan Wood, the only surviving clearly visible section is just inside the top Swan Lane entrance to the wood as well as a longer section which is not quite so discernible a short distance inside the bottom entrance to the wood from Swan Lane. Next time you are in the Wood have a look out for it.