Circumvallation

1. n. A line of field works made around a besieged place and the besieging army, to protect the camp of the besiegers against the attack of an enemy from without.
2. n. The act of surrounding with a wall or rampart.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.