Israel said throughout its 11-day Gaza bombing campaign that a prime target was the "metro" tunnel network that allowed militants of the Palestinian Islamist group Hamas to launch thousands of rockets.
In the face of a 14-year-old Israeli blockade, Hamas has been building a complex network of interconnected tunnels to conceal fighters and weaponry from the drones and warplanes that ensure the Jewish state's control of the skies, Israel says.
A tunnel network was dug under the border with Egypt, allowing the Iranian-backed Hamas and its Islamic Jihad allies to smuggle in arms, it says. Palestinians say the tunnels were a way for people and day-to-day supplies to get in and out of the besieged coastal enclave.
Egypt, facing a jihadist insurgency in the Sinai peninsula neighbouring Gaza, has flooded and destroyed most of the smuggling tunnels, while Israel's army bombed so-called "attack tunnels" leading into southern Israel during the last Gaza war in 2014.
"Since then, Hamas's main mission has been to develop a network of underground tunnels allowing movement across Gaza," an Israeli military official said, estimating the cost at $500,000 for each kilometre.
Shielded by up to 30 to 40 metres (100 to 130 feet) of earth, fighters and their commanders can move around and activate trap doors for rocket batteries metres underground to emerge then drop back out of sight, as seen in army videos.
"We don't know exactly where all these tunnels are... but we estimate we've destroyed about 100 kilometres of them," the military official said.
On Friday, a Hamas official, Mosheer al-Masry, played down any heavy losses.
"We say today that thousands of Qassam (military wing of Hamas) activists are now walking through the tunnels," he told reporters.
Strikes on homes
On the night of May 13-14, the Israeli army appeared to signal the launch of a land invasion to push militants into the tunnels and pummel them with heavy air strikes.
The strikes on the tunnels were deadly, Israel's Yediot Aharonot newspaper said, but those planning the air raids "failed to take into account the effect of the blast on the houses under which the tunnels were dug".
"The foundations of two houses in the Rimal neighbourhood were damaged, and the houses collapsed on the heads of their residents," it said of a seaside district of Gaza City, where residents have reported up to 200 strikes.
Just hours after a ceasefire took effect on Friday, emergency workers recovered five bodies and rescued around 10 survivors from the rubble of what appeared to be a tunnel hit by Israeli bombardment.
Prime Minister Benjamin Netanyahu hailed Israel's bombardment of Gaza as an "exceptional success".
"We achieved our goals in the operation," Netanyahu said, adding mysteriously: "The public doesn't know everything" about Israel's gains in the operation "and neither does Hamas".
Gaza's health ministry has put the death toll from Israel's air strikes at 243, including 66 children.
Israel launched its campaign in Gaza on May 10 in response to Hamas firing rockets into its territory, following weeks of escalating tensions between Israeli forces and Palestinians in Jerusalem.
Palestinian groups fired a total of more than 4,000 rockets at Israel, the Israeli army says, killing 12 people, including a teenager and a child, Israeli medics say.