When were they built and how many are they?
The construction of the tunnels started in Gaza before Israel withdrew its troops and settlers in the territory in 2005.
However, the tunnel network expanded at speed after Hamas took control of the Gaza Strip in 2007.
At its peak, there were almost 2,500 tunnels underneath the Egyptian border that Hamas and other militant groups used to smuggle in commercial goods, fuel, and weapons.
But Hamas and other factions started digging tunnels with the primary aim of attacking Israeli forces.
How long are these tunnels and where are they located?
The exact size of the tunnel network is difficult to assess as conflicting numbers have been floated around over recent years.
Following the last conflict in 2021, Hamas claimed its tunnels stretched a massive 500km. The IDF claimed it destroyed more than 100km of tunnels in airstrikes, while Hamas insisted only five percent were hit.
If the Hamas assessment of the tunnel network length is to be believed, it would be much bigger than the London Underground, which is 400km long and above ground.
The huge underground network of 40 or so tunnels spans several miles across the Gaza Strip, reaching the towns of Khan Younis, Jabalia, and the Shati refugee camp, while also stretching into Israel.
How deep underground do the tunnels go?
The tunnels underneath Gaza are believed to be as much as 100ft underground with entrances located on the bottom floors of houses, mosques, schools, and other public buildings that would allow militants to avoid detection.
The underground structures are reinforced with thick concrete to make them strong enough so they protect from air strikes and don’t collapse in the event of an attack.
Rare footage taken over the years from inside the network portrays a sweaty environment and not even tall enough for fighters to stand up straight.
But many others are well built, strongly reinforced, and even tall and wide enough for troops to sprint through or move contraband.
The tunnels are believed to have cost between £21million and $64million.
“The IDF has experienced these technologies, but they do have the ability to inflict serious casualties.”
Colin Clarke, research director at the New York-based Soufan Center think-tank, warned Hamas “knows its tunnels by heart”.
He said: “Some are probably booby-trapped. Preparing to fight in such terrain would require extensive intelligence, which the Israelis may not have.
“When tunnels are found, they can be closed off to shut in the people inside. In this case, the order is likely to be for no quarter to be given.”
