contravallation
(ˌkɒntrəvəˈleɪʃən) n (Fortifications) fortifications built by besiegers around the place besieged
[C17: from contra- + Latin vallātiō entrenchment; compare French contrevallation]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014