Students of urban warfare divide the battlefield into four planes. One is the sky above cities, increasingly thick with drones. Next are the buildings that extend upwards, offering vantage points and hiding places. A third is the streetscape: the lattice of roads, alleys and paths that form a city’s peacetime arteries. It is the fourth – the tunnels lying beneath – that will present the greatest challenge to the Israel Defence Forces (IDF) when they begin their invasion of the Gaza Strip in the coming days.

The first smuggling tunnels in the area were built by Bedouin clans on both sides of the Egypt-Gaza border after 1981, when Israel and Egypt demarcated the border. The first known tunnel attack from the strip occurred in 1989. But it was in 2001 that Hamas, the militant group that would later take over the territory, after Israel withdrew in 2005, began construction of a remarkable subterranean network. Its initial aim was to smuggle in material and arms from Egypt. But the tunnels had manifold other uses.