SEA-ME-WE 4 and
FLAG are both fiber optic cables that run from Europe to Asia. They are mostly under water, with runs across land when they have to. Neal Stephenson did an excellent
article in Wired in 1996 about the people working on laying the fiber for FLAG. On Jan 30, both the SEA-ME-WE 4 and FLAG cables were cut,
disturbing many Middle Eastern and Asian countries' internet access.
I highly recommend reading the wired article, it's a fascinating explanation of the how and whys of underwater telecommunication industry.