The tunnels under Gaza are best known as passages used to smuggle goods from Egypt and attack Israel.

But there is a second underground network that the Israel Defense Forces colloquially refers to as the “Gaza Metro,” according to CNN.

It is a vast maze of tunnels, several kilometers long, used to transport people and goods, store rockets and ammunition depots, and house Hamas command and control centers, all of which are protected from aviation and IDF surveillance drones.

In 2021, Hamas claimed to have built 500 kilometers of tunnels under Gaza, although it is unclear whether this figure was accurate or bravado.

If true, Hamas’ underground tunnels would be just under half the length of the New York subway system.

“It’s a very complex, very large — huge — network of tunnels in a fairly small area,” said Dafna Richemond-Barak, a professor at Israel’s Reichman University.

It is unclear how much money Hamas, which rules the impoverished coastal strip, has invested in the network. The figure is likely to be significant, both in terms of labor and capital.

Gaza has been under a land, sea and air blockade by Israel since 2007, as well as a land blockade by Egypt, and Gaza is believed to lack the massive machinery normally used to build deep underground tunnels.

Experts say workers are using rudimentary tools, likely digging deep underground, to build the grid, which has electricity and is reinforced with concrete.

Israel has long accused Hamas of diverting concrete intended for civilian and humanitarian purposes to build tunnels.

Hamas critics also argue that the large sums used to build the tunnels could have been used instead for civilian bomb shelters or early warning networks similar to those on Israel’s border. (complete on CNN)