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An Israeli army officer shows journalists a Palestinian tunnel that runs from the Gaza Strip into Israel. Israel says its current military campaign is aimed at destroying the tunnels.
The stated objective of Israel's campaign in Gaza has been to destroy a network of underground tunnels that Hamas uses to stage incursions into Israel.
Militants have attacked six times through tunnels during the course of recent fighting and the Israeli military says they have uncovered at least two dozen tunnels with more than 60 entry points.
Beyond the tactical utility of the tunnels, they have had a powerful psychological grip on the Israeli public. And in fact, tunnels have been a staple of asymmetrical warfare for thousands of years.
Professor Wayne Lee, author of "Barbarians and Brothers" and professor of history at University of North Carolina, Chapel Hill, said some of the earliest examples of tunneling can be found as far back as the Assyrian civilization in the 7th and 8th centuries, B.C.
According to Lee, the tunnels began as a response to large walls and fortresses, where any ground attack could be easily seen and prevented by armed guards on top. There is art depicting Assyrian troops attacking the foundations of walls from underneath.
There is also archaeological evidence from the late Roman Empire of tunnels used by the Persians to take the city of Dura-Europos in present-day Syria. Lee said the Persians were digging a tunnel to penetrate the city. The Romans dug a counter-mine to meet them but the Persians became aware of their enemy's mine and released sulphur dioxide gas to kill them. Remains of Roman soldiers were excavated in these tunnels.
Tunnels were also famously used by the Viet Cong during the Vietnam War to gain advantage over better-resourced enemy, the U.S. While the U.S. had air power to surveil for troops, the Viet Cong guerillas would hide soldiers and equipment in tunnels to avoid detection before ambush.
In the current conflict in Gaza, Lee said the network of tunnels began as an economic lifeline to bring in supplies barred by the blockade of Gaza. The tunnels can easily be converted to military use, but they don't pose a serious threat to the overall security of Israel due to the limited number of people and weapons that can fit through them.
"These are sites of pinprick level attacks," said Lee. "But they have this psychological consequence because they violate our norms of what a nation is supposed to provide, that is a border security."