The Thorn Hedge is a defensive system of Mechanicsburg controlled by Castle Heterodyne. It is comprised of massive thorny vines erupting from the ground around the standard town wall that can be rapidly grown on command to form a nigh-impenetrable barrier. During the climactic moments of the Siege of Mechanicsburg, Castle Heterodyne deploys the Thorn Hedge. Sprouting with such speed and force it can throw heavily armored vehicles, such as a Toothy Tank. Without Castle control, the vines can grow wildly unchecked, as they did when the Take Five Bomb froze the castle in time (though how "frozen" the Castle actually is is .) This feature was originally installed by Agatha's great-great-grandfather, and has caused the hedge to envelop the entire containment complex surrounding the town that had been built during the Timeskip. 
Note on Nomenclature Edit
The inscrutable Higgs has proving that they are a defense native to the town, although they might be enhanced by the newly restored castle. As he called them Thorn Hedge this pages name has been changed from Iron Briars to reflect in-story terminology.
- ↑ http://www.girlgeniusonline.com/ggmain/doublespreads/ggcoll13_126_127.html
- ↑ Reddit Ask-Me-Anything, 30 May 2013:
PKSchefflera: Was the in the Storm King opera actually a stage translation of Mechanicsburg's thorn wall?'
'Phil: It is now.'