defense structure, estimated to be 3,100 miles upon completion. The wall included watchtowers built at intervals, with a sophisticated warning and communication system of smoke signals, lanterns, and beacon fires.

Though the Great Wall slowed the attacks, this passive strategy was not enough to end the assaults of the fierce Xiongnu horsemen who often rode in groups of up to 300,000 archers. Roughly 100 years later, Emperor Wudi initiated an active campaign against the barbarians, to finally end their attacks. By sending out strong expeditions to disband the barbarian warrior groups at their sources, the Chinese finally established absolute rule for a period. This historical experience illustrates the need to supplement a passive protective strategy with an effort to actively engage a threat at its source.

In modern history, Israel embraceda similar method for protection by building a 100-mile line of defensive walls and trenches along the eastern side of the Suez Canal to protect Israelis from Egyptian artillery bombardment during the War of Attrition (1967--70). It was estimated that Israel invested \$300 million in this massive defensive concrete and sand structure called the Bar Lev Line, reaching a height of 66--82 feet \[[@CR2]\]. Just behind the line was the first line of fortification with 22 forts resembling 31 strongpoints. Each strong point was supported with trenches, minefields, barbed wire and up to 26 bunkers armed with medium to heavy machine guns. Israel took almost every possible and potential threat into consideration as they built the line, even considering the installation of an underwater pipe system to pump