Hundreds of tunnels under the border between the Gaza Strip and Egypt are keeping many of the Palestinian territory’s 1.5 million impoverished residents supplied with food and fuel.
Sources say there are more than 6,000 Palestinians employed in the clandestine industry, which merchants say is heavily controlled by the Hamas authorities.
Strict rules are imposed on what can be brought in - weapons, drugs and people-trafficking are prohibited - and tunnel operators are taxed.
The tunnels were previously used to smuggle weapons to fight the Israeli occupation, but the blockade that was enforced after Hamas seized control of the Gaza Strip in 2007 has made the smuggling of basic supplies a necessity.