Tier 3 — Mill

This is the tier most reconstruction plans skip, and it is the one that actually decides whether you plateau. Steam without precision boring is a bomb. Chemistry without glassware is guesswork. Everything above depends on the machine tools built here.

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Mill

Medieval to early modern Year 8 – Year 30 ≥ 300+ people

Put something other than muscle to work, and start making machines that make machines.

Energy used: about 26,000 kcal per person per day, Cook's advanced agricultural stage (AD 1400) · where civilization stands

Binding constraint. The binding constraint is precision. A water wheel is easy; a water wheel driving a lathe that cuts a true cylinder is not. You cannot make a tool more accurate than the tool that made it — except through a handful of self-referential tricks, and until you know them you are stuck at the accuracy of your hands.

Overshot wheels at the Hexenloch mill — the first power that is not muscle.

t3-waterpower

Water power

Get a source of continuous power that is not a muscle.

Energy Guide ×4BuildSheet ×21

A full set of sails with their shutters closed. The sail is twisted along its length — steeper at the hub, nearly flat at the tip — because the tip travels several times faster and meets the wind almost edge-on.

t3-windpower

Wind power

Get continuous power where there is no falling water — which is most places.

Energy Guide ×2BuildSheet ×23

A flight of locks at Dunardry on the Crinan Canal, seen over the balance beams of one pair of gates to the next lock up. Each chamber lifts a boat a few metres; a flight climbs a hill in steps.

t3-canals

Canals and locks

Carry bulk goods by water where no river goes, and lift boats over hills.

Transport Guide ×2Sheet ×7

The barque Picton Castle under full sail: square sails on its masts, and fore-and-aft sails between them.

t3-ships

Seagoing sailing ships

Build and sail decked ships that cross open sea with cargo and crew, without capsizing, sinking or losing the crew to scurvy.

Transport Guide ×2Sheet ×7

A hot-air balloon in flight, 2021: the basket hangs below the open mouth, the burner between them.

t3-balloons

Balloons

Lift a load with heated air or a light gas, tether it for observation or signals, and know exactly how much it can carry and what makes it burn.

Transport GuideBuildSheet ×5

A centre lathe. Machines that make machine parts are the hinge of the whole ladder.

t3-machinetools

Machine tools and precision

Build machines that make machines — and break the accuracy ceiling.

Tools Guide ×3Build ×3 0.1 mm → 0.01 mm

Rolled steel reinforcing bar. Iron becomes structural once carbon and heat treatment are controlled.

t3-steel

Steel and heat treatment

Make metal hard enough to cut other metal.

Materials Guide ×2Build 900–1,100 °C

Cement being mixed on site. A binder that sets under water changes what can be built.

t3-cement

Cement and concrete

Make artificial stone you can pour into any shape.

Materials Guide ×4BuildSheet ×10 1,400–1,450 °C

t3-glass

Glass

Make a transparent, chemically inert, formable solid.

Materials Guide ×2Build ×2 1,100–1,500 °C

A small glasshouse on a brick base with a row of cold frames in front of it, in the botanic garden at Leuven, Belgium.

t3-glasshouse

Cold frames, hotbeds and the glasshouse

Raise transplants before the last frost and keep tender crops growing after the first, under glass warmed by the sun, by rotting manure and by a wall that holds the day's heat.

Food GuideBuild Sow at 24 °C in the hotbed soil

Sheep strip-grazing a field of turnips (2021): an electric fence is moved forward a strip at a time, so the flock eats the crop where it grew and dungs the field for the cereal that follows.

t3-rotation

The four-course rotation, field drains and the seed drill

Run the fields as one system: a rotation whose fodder crops feed the stock and whose manure feeds the grain, wet land underdrained so it can be worked and sown, and grain drilled in rows at a known rate and depth so it can be counted and hoed.

Food GuideSheet

Raising a timber-frame bent, 2008: posts, tie beam, rafters and diagonal knee braces joined flat on the ground, then lifted and stood up as one piece.

t3-frame

Framed and glazed building

Frame a building in timber on a masonry plinth, brace it so it cannot rack, glaze its windows, and keep it dry, warm and ventilated.

Shelter Guide ×4Sheet ×10

t3-acid

Acids

Make sulphuric acid, and with it most of industrial chemistry.

Materials Guide ×3

Plant at a soda ash works. Alkali underpins soap, glass, paper and textiles at once.

t3-alkali

Alkalis

Make soda ash and caustic soda at scale.

Materials Guide ×2

A voltaic pile in the Tempio Voltiano, Como: a stack of alternating zinc and copper discs with brine-soaked separators, held in a wooden frame, with a copper strip leading off each end.

t3-battery

Batteries: from the voltaic pile to the lead-acid cell

Make a steady electric current from chemicals — for the telegraph, plating and electrolysis — before there is any generator.

Energy Guide Zinc boils at 907 °C; distil it at 1,100–1,200 °C

t3-paper

Paper

Make a cheap, plentiful writing surface.

Knowledge

Metal movable type in the case. Copying stops being the bottleneck.

t3-printing

Printing

Make copies faster than people can write them.

Knowledge

Washing hands. The single cheapest intervention in the history of medicine.

t3-germ

Germ theory and antisepsis

Establish that disease is caused by organisms — and act on it.

Health Guide ×6Build

Making up chlorine solution at a water collection point in Awerial, South Sudan, 2014: the product goes into a small marked bucket, with a basin of river water behind, before it is added to collected water.

t3-chlorine

Make chlorine disinfectant

Make sodium hypochlorite from salt, water and direct current, measure its strength, and dose drinking water so that 0.2–0.5 mg/L of free chlorine remains 30 minutes later.

Water Guide ×2Sheet Brine 20–27 °C at the start; keep the cell below 35 °C Free chlorine 0.2–0.5 mg/L at the collection point, 30 minutes after dosing

A theodolite. You cannot build to a tolerance you cannot measure.

t3-instruments

Instruments and measurement

Turn observation into numbers.

Knowledge Guide ×5Build ×2 Repeatable to 1%

French cast-iron metric weights of 5 kg, 2 kg, 1 kg, 500 g and 200 g: the 1, 2, 5 series, with the value cast into each top.

t3-units

One metre, one kilogram, everywhere

Fix the units, hold the standards, and make every measurement comparable to every other.

Knowledge Guide ×4

An experiment on a bench. The controlled comparison is the machine that makes reliable knowledge.

t3-method

Controlled comparison and the negative result

Establish how you decide whether something is actually true.

Knowledge Guide

An 1830s account book. Double entry makes an enterprise auditable by someone who was not there.

t3-ledger

Double entry and the auditable enterprise

Keep accounts a stranger can check.

Economy Guide ×2

A coining screw press at the Germanisches Nationalmuseum, Nuremberg: the weighted bar swings the screw down to strike the blank between two dies in one blow.

t3-coin

Fungible token and the mint

Strike coins of a weight, fineness and size fixed in law, at one mint working under seal, and prove every year, in public, that they meet the standard.

Economy Guide Every coin within the weight, size and fineness limits the law sets, shown by the yearly public trial

A Sumerian contract for the sale of a field and a house, Shuruppak, about 2600 BC. Price, parties and witnesses written into clay: the enforceable promise is older than coinage.

t3-contract

The enforceable promise

Make a promise between strangers as reliable as one between kin, by writing it down and having a court enforce it quickly and cheaply.

Society Guide

A childhood vaccination. Health becomes a public system rather than a private accident.

t3-publichealth

The health authority

Give someone the standing, the information and the power to act on disease before it spreads.

Society Guide ×5

Brick terraces at Am Salzhaff, Wismar, Germany (2018): the party walls rise through the tiled roofs as parapets, so fire in one roof space cannot run along the row.

t3-fire

Fire separation and the building code

Write and enforce a building code that stops a fire in one building from reaching the next, gets everyone out of the building it starts in, and puts enough water within reach of every building.

Settlements Guide Party wall at least 375 mm above the roof; escape window at least 0.33 m² and 450 × 450 mm