A couple of months ago we looked at what the Fremen ate, and a couple of weeks back we explored Fremen tech.

And while it's not a nifty little personal device, the latter piece should’ve included the real pinnacle of Fremen technology: the sietch.

So I decided to correct that oversight by talking about what they are and also trying to do a comprehensive list of all the named sietches on Arrakis.

In short, a sietch is a moisture-sealed cave complex that can shelter literal thousands while staying completely invisible from the outside; an entire city of people hidden inside a mountain, producing everything the community might need.

A sietch operates simultaneously as fortress, factory, and family unit.

Ideally, a sietch entrance is a narrow, defensible passage.

It’s deliberately designed to be held by a few defenders against much larger forces, while the internal layout provides multiple escape routes so inhabitants never get trapped in a siege.

The cave systems themselves are usually carved from living rock using cutterays. Natural caverns are expanded and connected by hand-carved tunnels, creating long, labyrinthine complexes that can shelter not just the population of a sietch but the production the community requires to survive.

Sietches function as complete industrial centers - while being buried underground.

Manufacturing floors produce stillsuits and fremkits, and maula pistols, while textile operations weave fabric from desert cotton and whatever else is available - including human hair.

Food processing centers handle everything from underground plantations to whatever protein sources the desert provides.

But Spice doesn’t only end up in food. Its residue is turned into substrates for fabrics, plastics, and even explosives.

The production facilities, like human life, require a lot of water. Deathstills handle the grim but necessary business of water recovery from human remains, while windtraps capture what minimal humidity there is in Arrakis's dry air.

All of this results in the sietch being a self-sufficient community. Self-sufficient and moisture-sealed - which means it has a distinct odor.

While we’d usually think of a place, the sietch also signifies a fundamental social unit in Fremen society. We know this from how every member of the tribe has an internal and external name: Paul is known to everyone in Sietch Tabr as Usul but as soon as outsiders are present, he’d be called Muad’Dib.

The sietch as a tribe is counted not in individuals, but hearths.

But just like with the names, internally the Fremen referred to their private spaces differently.

Sietches also have organized education. Not only that, they have classrooms with chalkboards.

Most of the things we know about how sietches operate come from descriptions of the most famous of all sietches: Sietch Tabr.

It was considered one of the bigger and more prosperous communities and was one of the many sietches that had a hidden cache of water reserves - at the time of Paul’s arrival it contained 38 million decaliters, to be precise.

While the Harkonnen’s return after the battle of Arrakeen and Rabban’s pogrom forced an evacuation of the place, it seems the name travelled with the people because Stilgar’s new sietch in the south was still referred to as Tabr by the end of Dune.

By the time of Children of Dune, (the original) Sietch Tabr had undergone major modifications. Traditional moisture-sealed construction was supplemented with new buildings made of mud brick and transparent windows.

Stilgar considered these changes an offense against traditional design, but they showed the sietch's evolution from hidden refuge to administrative center. The sietch now worked as part of the royal household where Stilgar served as guardian of Paul's orphaned twins, Leto and Ghanima.

And speaking of Leto II, once the Fremen were all but part of a museum exhibit, he used Sietch Tabr as the hiding place for his massive spice hoard. The God Emperor concealed melange throughout the entire great chamber and surrounding passages, creating a reserve worth more than most planetary economies. By this time, the location was called "Tabur," with its outlines still visible but transformed by a water-rich environment.

When Darwi Odrade explored the ruins in Heretics of Dune, she found ninety thousand long tons of spice - equivalent to half a year's harvest from the planet then called Rakis - and Leto’s secret diaries.