WHEN Cyrus Field, an American businessman, laid the first trans-Atlantic cable in 1858, it was hailed as one of the great technological achievements of its time and celebrated with bonfires, fireworks and 100-gun salutes. Alas, the reason for the festivities soon went away. Within weeks the cable failed.

On September 21st the completion of another trans-Atlantic cable was welcomed with much less ado. But it is remarkable nevertheless: dubbed Marea, Spanish for “tide”, the 6,600km bundle of eight fibre-optic threads, roughly the size of a garden hose, is the highest-capacity connection across the ocean. Stretching from Virginia Beach, Virginia, to Bilbao, Spain, it is capable of transferring 160 terabits of data every second, the equivalent of more than 5,000 high-resolution movies. Facebook and Microsoft each own 25% of Marea, and the rest is owned by Telxius, a telecom infrastructure firm that is controlled by Spain’s Telefónica.

Such ultra-fast fibre networks are needed to keep up with the torrent of data flowing around the world. In 2016 traffic reached 3,544 terabits per second, roughly double the figure in 2014, according to TeleGeography, a market-research firm. And demand for international bandwidth is growing by 45% annually. Much traffic still comes from internet users, but a large and growing share is generated by big internet and cloud-computing companies syncing data across their networks of data centres around the world.

These firms used to lease all of their bandwidth from carriers such as BT and Level 3. But now they need so much network capacity that it makes more sense to lay their own dedicated pipes, particularly on long routes between their data centres. The Submarine Telecoms Forum, an industry body, reckons that 100,000km of submarine cable was laid in 2016, up from just 16,000km in 2015. TeleGeography predicts that a total of $9.2bn will be spent on such cable projects between 2016 and 2018, five times as much as in the previous three years.

Owning a private subsea fibre-optic network has several advantages, including more bandwidth, lower costs, and reduced delay, or “latency”. Having access to multiple cables on different routes also provides redundancy. If a cable is severed—by fishing nets, sharks, or an earthquake, among other things—traffic can be rerouted to another line. Most important, however, owning cables gives companies greater say over how their data traffic is managed and how equipment is upgraded. “The motivation is not so much saving money. It’s more about control,” says Julian Rawle, a submarine cable-industry expert.

Some people worry that owning the pipes that carry their customers’ data will give big tech firms even more power than they already have, likening the situation to Amazon’s owning the roads on which its packages are delivered and the lorries that carry them. Others fret that conventional network operators may struggle to adapt their business models, as companies such as Facebook are moving onto their turf. “Within the next 20 years,” predicts Mr Rawle, “the whole concept of the telecom carrier as the provider of the network is going to disappear.”

Correction (October 19th 2017): The original version of this article failed to mention that Telxius, controlled by Spain’s Telefónica, owns half of Marea, along with Facebook and Microsoft, which each have 25%. Sorry.