Last October, UN officials said the construction and use of smuggling tunnels between the Gaza Strip and Egypt had grown to such an extent that it amounted to an industry.
The UN said tunnels had become a lifeline because of the tight blockade on Gaza. Thousands of Palestinians owe their living to the tunnelling business in places like the border town of Rafah.
The tunnels are used to smuggle a wide variety of products into Gaza - including cigarettes, food, fuel, fridges and clothes which are for sale in the border town of Rafah.
Even animals make the journey through the tunnels, and not just livestock for Gaza's farms or dinner tables. Rafah boasts its own zoo, whose exhibits, including three young lions, have been smuggled in.
In September, the Hamas group which controls Gaza introduced regulations to license and control trade through the tunnels, even supplying phone and electricity connections.
In addition to staple goods smuggled under the border, militant groups are also believed to have smuggled quantities of weapons into Gaza.
Egyptian police regularly seize tunnel-making equipment along the border with the Gaza Strip. Israel has accused Egypt of not doing enough to prevent the flow of weapons.
But on the Gaza side of the border, in Rafah town, the equipment is usually readily available from street traders who sell their wares out of wheelbarrows.
The smuggling tunnels have been heavily pounded by Israel during its bombardment of Gaza which began on 27 December. The Israeli military said it hit 40 tunnels in the first two days.
Many tunnels will have been put out of action, but as Rafah depends so heavily on illegal smuggling it seems unlikely that those who excavate them will give up their trade.