Below Gaza

Palestinians see them as Gaza's lifeline, Israelis as a dangerous thoroughfare for weapons and fighters: the several hundred, or maybe even thousand, tunnels that connect closed-off Gaza to the rest of the world. Even animals are taken through the corridors, which are often only waist-high.

Roughly 1.8 million Palestinians live in Gaza. They are separated from neighboring Israel and Egypt by high walls and heavily fortified borders and are thus completely isolated. For a long time, the Rafah border crossing to Egypt was the only possible way to enter or exit the territory. But after Hamas rose to power in Gaza in June 2007, this has been closed as well.

Ever since then, the tunnels are the only connection to the outside world. They are often built with simple means like shovel and pickaxe and held up with wooden boards. Larger tunnels are wainscoted with concrete. For young Palestinians, the construction work is one of the few ways to make money - but deaths belowground occur again and again.

The tunnels' entry points are often hidden in regular houses, so that they can't be seen from the outside. Everyone who wants to use them has to pay for it, and the house owners get a part of the earnings. Israelis say that the money people in Gaza pay for the tunnels could be better used for other needs.

The Palestinians use the tunnels to bring cement and other construction materials into the Gaza Strip to maintain and expand their infrastructure. Consumer goods like clothes and groceries travel through the corridors - as do rockets and explosives. Fighters even dig tunnels underneath Israeli military bases and blow them up from below.

The tunnels have existed in Gaza for more than 30 years. After the 1979 peace treaty between Israel and Egypt, the southern city of Rafah was divided: One half belonged to Egypt, the other to Gaza. Exchange between the two sides of the divided city was organized via tunnels. And with time, the illegal subterranean network was expanded.

Today, even some of the simpler tunnels have sophisticated infrastructure. There's electricity and telephones, so the construction workers can keep in touch with the world aboveground. When the Israeli army attacks, the tunnels also function as shelters and hiding spots.

Israel is not the only state fighting the tunnels. Egypt also opposes them, because the Sinai Peninsula keeps seeing attacks which are allegedly carried out by Hamas. That's why the Egyptian army has destroyed tunnels on their territory for years. Even the Muslim Brotherhood government under now ousted President Morsi, which is politically close to Hamas, took actions against the tunnels.

Many tunnels are used for the sole purpose of killing Israeli soldiers. In the past, militants have dug tunnels underneath Israeli military bases and then blown them up. This picture, published by Hamas in 2004, shows the explosives used in December of that year to set off an underground explosion that killed five IDF soldiers and wounded 10 more.

Moshe Yaalon, Israel's defense minister, visited a well developed tunnel leading from Gaza to Israel in 2013. According to Israel, the tunnel was used for attacks by Hamas and for kidnapping Israeli citizens.

Israel claims to have discovered and destroyed several dozen tunnels since the start of the ground offensive in Gaza. Israeli Prime Minister Benjamin Netanyahu disregarded international calls for a ceasefire and said the military offensive against Hamas would continue: "We won't end the mission before we have destroyed the tunnels."