CNN reports that the tunnels under Gaza, known as the "Gaza metro," serve a variety of purposes for Hamas. These tunnels are used to transport people and goods, store rockets and ammunition, and house command and control centers for Hamas away from surveillance drones. It is estimated that Hamas has built around 500 kilometers (311 miles) worth of tunnels under Gaza, although the accuracy of this claim is uncertain. The tunnel network is a complex and expansive system that spans a relatively small area. It is likely that the construction of these tunnels required significant manpower and capital for Hamas. Gaza has been under blockade by Israel and Egypt since 2007, making it difficult for the region to possess the heavy machinery typically used for tunnel construction. Instead, it is believed that Hamas used basic tools to dig these tunnels deep underground, reinforcing them with concrete and wiring them with electricity. The asymmetric advantage provided by these tunnels allows Hamas to level the playing field in their conflict with the more technologically advanced Israeli military.