Thin underwater cables hold the internet. See a map of them all.

Submarine fiber-optic cables remain the preferred backbone for high-speed international data because they deliver far higher capacity and lower latency than satellite or balloon systems, making them the practical choice for large-scale, time-sensitive traffic.

Because early undersea cables lay in shallow, accessible waters without robust protection, surface vessels and fishing gear frequently collided with or severed them, causing major service interruptions.

Early submarine telegraph cables were coated in waterproof organic substances—like exotic tree sap—because those sealants were the best available way to stop seawater from corroding conductors before modern synthetic insulators existed.

Submarine cables developed as a logical extension of telegraph networks because engineers scaled continuous electrical links from small demonstrations to city-wide lines along rail corridors, making it technically straightforward to run those links under water to connect distant places.

Ships bury cables by dragging a plow that lays the line into a narrow seabed groove, and ocean currents then refill the trench with sand, which naturally shields the cable from surface hazards.

Because they lie on or near the seafloor, submarine cables are exposed to environmental forces and marine life that can damage them—earthquakes can shear cables and animals have been known to bite or abrade the lines.

Submarine cables use only a few protective layers—like insulation and petroleum jelly—because those barriers stop seawater from entering and chemically degrading the fibers while keeping the cable flexible.

Undersea fiber-optic cables carry most international data because continuous fiber lines laid across the ocean floor create high-capacity, low-loss pathways that directly link continents and handle cross-border internet traffic.