Why capital cities end up where they do

Ask someone to name the biggest city in Australia and they'll say Sydney, which is right. Ask for the capital and a decent proportion will say Sydney again, which isn't. It's Canberra, a city of under half a million people that didn't exist in 1910.

The same trap catches people out with Brazil, Canada, Turkey, Switzerland, Nigeria, Myanmar and the United States. That's not a coincidence, and it isn't a quirk of quiz-setting either. Capitals get placed for reasons, and they're usually geography, defence, money or an argument between two rival cities that nobody was going to win.

Most of them are still visible if you know what you're looking at.

The oldest reason is that somebody could hold it

Before a capital was an administrative convenience it was a stronghold. The court sat where the ruler could survive a bad year, and that meant high ground, a river bend, a marsh, an island, or a rock. It didn't have to be comfortable.

Athens grew around the Acropolis, which is a defensible limestone outcrop with a water supply on top. Rome sat on hills above a crossing of the Tiber. Moscow's Kremlin is a fortified triangle on a rise where the Neglinnaya met the Moskva. Edinburgh's castle is on a plug of volcanic rock that a glacier failed to remove. Athens, Rome and Moscow all outgrew the fort by an enormous factor, but the fort is why the city is there and not fifteen miles away.

Islands and lagoons did the same job. Paris started on the Île de la Cité, a defensible island in the Seine, and spread onto both banks afterwards. Mexico City sits on what was Tenochtitlan, built on an island in a lake, reachable only by causeways that could be cut — which is exactly what the Aztecs did during the fighting in 1520.

Then the guns got better and the walls stopped mattering. What didn't stop mattering was water.

Rivers, and specifically the awkward bits of rivers

Cities cluster where a river becomes a problem, because that's where the money is.

The classic case is a bridging point. London sits roughly at the lowest place the Thames could be bridged with Roman engineering — downstream of that it's too wide and too tidal, upstream you're going out of your way. Everything crossing the river in the south-east of England had to funnel through one place, and a place that everything funnels through collects tolls, markets, warehouses and eventually a government.

The head of navigation does the same trick in reverse. That's the point where seagoing ships have to stop and unload onto something smaller — usually a fall line, where rivers coming off harder upland rock drop onto a coastal plain. On the eastern seaboard of the United States there's a whole line of cities strung along it, Washington among them, sitting where the Potomac stops being navigable.

Add ports, which need shelter, depth and a hinterland worth trading with. Lisbon has the Tagus estuary. Copenhagen sits on the strait every ship between the Baltic and the North Sea has to squeeze through, and charged them for the privilege for four hundred years. Buenos Aires is on the Río de la Plata. Colonial capitals in Africa are almost all ports — Lagos, Accra, Dakar, Luanda, Maputo — because the point of the administration was to move goods to Europe, not to govern the interior conveniently. Several of those countries have since moved their capitals inland, and that's the reason why.

Sometimes the argument is just about the middle

Once a state is big enough that officials have to travel, being roughly equidistant from everywhere starts to beat being on the coast.

Madrid is the cleanest example in Europe. It was a modest town of no great importance when Philip II moved the court there in 1561, and its main qualification was sitting near the geometric centre of Iberia, on a plateau, not obviously belonging to Castile's rivals. Spain has better ports, better rivers and better farmland almost anywhere else. It has its capital in the middle of a dry tableland because that was the point.

Altitude counts too, in the tropics. Bogotá, Quito, Addis Ababa and Mexico City are all at heights that would be uninhabitable in a colder latitude and are pleasant where they are — cool, less malarial, and generally where the pre-colonial population was already concentrated. Nobody put those capitals in the highlands for the view, and they aren't there by accident.

Compromise capitals, or how to stop two cities fighting

The most interesting capitals are the ones nobody actually wanted. They exist because two rivals each preferred a neutral third option to letting the other one win.

Washington came out of a bargain in 1790. Northern and southern states were at odds over both the location of the seat of government and a proposal for the federal government to take on the states' war debts. The Residence Act settled the capital on a site on the Potomac, between north and south and next to Virginia, with George Washington choosing the exact spot; the debt assumption passed alongside it. The district was carved out of Maryland and Virginia so it wouldn't belong to any state — which is also why residents of Washington DC still don't have voting representation in the Senate.

Ottawa was picked by Queen Victoria in 1857. The Province of Canada had been shuttling its government between Kingston, Montreal, Toronto and Quebec City, which was expensive and satisfied nobody. Ottawa was small, it sat almost exactly on the line between Canada West and Canada East, it was defensible, and it was further from the American border than Toronto or Montreal — a live concern at the time. The choice was mocked as absurd at the time. It's still there.

Canberra is the most deliberate of the lot. When the Australian colonies federated in 1901, Sydney and Melbourne both wanted the capital and neither would concede. The constitution split the difference in writing: the capital would be in New South Wales, which satisfied Sydney, but at least a hundred miles from Sydney, which satisfied Melbourne — and Melbourne would host the government until the new city was ready. A site on the Limestone Plains was chosen in 1908, an international design competition was won in 1912 by Walter Burley Griffin and Marion Mahony Griffin from Chicago, and Parliament finally moved in 1927. Melbourne had the seat of government for twenty-six years while everyone waited.

Brasília is the boldest. A capital in the interior had been proposed since the 1820s and was written into the 1891 constitution, and nothing happened for decades because it was obviously impractical. Juscelino Kubitschek made it a campaign promise, and the city was built on empty savanna in about four years, laid out by Lúcio Costa with the major buildings by Oscar Niemeyer, and inaugurated on 21 April 1960. Rio de Janeiro lost the capital it had held since 1763. The stated aim was to pull development and population away from the crowded coast and into the middle of the country, and by any measure that partly worked — the population of the surrounding Federal District is now well over three million.

Building one from scratch has a cost

Planned capitals share a set of problems, and they show up reliably.

• They're expensive, and the money has to come from somewhere while the city produces nothing.
• They're designed for a projected population and a projected way of living, and both projections are guesses. Brasília was laid out for cars in an era when far fewer Brazilians owned one, and the low-density plan pushed poorer workers into satellite towns outside the designed area almost immediately.
• Civil servants generally don't want to move. Governments have had to offer allowances, housing and outright orders to shift departments.
• The old capital keeps the banks, the newspapers, the universities and the social life, and often keeps real power for a generation or more.

Islamabad was built through the 1960s to replace Karachi, planned by the Greek architect Constantinos Doxiadis, sited in the north near Rawalpindi and the military establishment. Abuja was designated in 1976 and formally took over from Lagos in 1991, chosen for being central and for not belonging to any of the country's major ethnic groups. Tanzania designated Dodoma in 1973 and then took over forty years to actually finish moving from Dar es Salaam. Kazakhstan shifted its capital from Almaty in the far south-east to a cold town on the northern steppe in 1997. Myanmar moved the government from Yangon to Naypyidaw in 2005 with almost no public warning, and the new city has famously wide and famously empty roads.

Côte d'Ivoire is the awkward one. Yamoussoukro has been the official capital since 1983 — it was the president's home village — but the government, the embassies and the business have largely stayed in Abidjan. Having a capital on paper and a different one in practice is more common than you'd think, and it's rarely tidy.

Capitals move when the map changes

A capital is a bet on where the centre of a country is. Sometimes the country moves and the bet doesn't hold.

Peter the Great founded St Petersburg in 1703 on marshland captured from Sweden, and made it the capital in 1712, deliberately turning Russia to face the Baltic and Europe. It held the job for two centuries. In 1918, with a world war on and German forces uncomfortably close to the coast, the Bolsheviks moved the capital back to Moscow — inland, further from any front line, and better connected to the rest of the country by rail.

Turkey did something similar in 1923. Istanbul had been the imperial capital for centuries and sits on a strait that had just been occupied. Ankara was an inland town on the Anatolian plateau that had served as the base of the nationalist movement during the war of independence, and moving the capital there was a statement about what the new republic was going to be as much as a security decision.

Japan moved its capital repeatedly for reasons that were often as much about escaping entrenched interests as anything else — Nara to Kyoto in 794, and Kyoto to Edo in 1868, at which point Edo was renamed Tokyo, meaning eastern capital. Germany made Bonn the provisional capital of the west in 1949 precisely because it was small and unimportant, so nobody would mistake it for a permanent settlement; the Bundestag voted narrowly in 1991 to move back to Berlin after reunification, and it wasn't finished for most of the decade.

Some countries don't bother having just one

The idea that a country has a single capital city is a convention, not a rule, and several places ignore it.

South Africa splits the job three ways as a legacy of the 1910 union between formerly separate territories: the executive sits in Pretoria, Parliament in Cape Town, and the supreme court of appeal in Bloemfontein. Cabinet ministers and civil servants shuttle between two of them, which is as inefficient as it sounds, and it's survived every proposal to fix it.

Bolivia has Sucre as the constitutional capital and the judiciary, and La Paz as the seat of government and legislature — the result of a civil war in 1899. The Netherlands names Amsterdam as the capital in its constitution while the government, the parliament and the monarch's working palace are all in The Hague.

And Switzerland, characteristically, refuses to name a capital at all. Bern is the federal city and holds the government. The constitution doesn't call it the capital, because agreeing on one would have meant Zurich, Geneva and Basel losing an argument.

Why the capital is so often not the biggest city

Put the two lists side by side and roughly a third of countries have a capital that isn't their largest city. That's not random.

The largest city is usually the one with the best port or the best position on a trade route, which is a commercial logic. The capital is chosen by a political logic, and the two frequently disagree. When a country picks a compromise site, or an inland site, or a defensible one, it's explicitly choosing something other than the biggest existing city — that's the whole point of the exercise.

There's a counter-pressure, though. Being the capital is itself an economic engine. Embassies, ministries, courts, lobbyists, contractors, journalists and everyone who feeds them all cluster around government, and in a centralised state that snowball gets very large. Mark Jefferson noticed this in 1939 and called it the law of the primate city: in many countries the largest city is not just biggest but disproportionately biggest, several times the size of the second. Paris against Lyon, London against Birmingham, Seoul against Busan, Bangkok against anywhere in Thailand.

Which cuts both ways. A capital deliberately placed somewhere neutral doesn't stay neutral, because it grows.

What to actually look for

Take any capital and the placement usually falls out of one of five things, sometimes several at once.

• Defence. A hill, an island, a river bend, or simply a long way from a hostile border.
• Water. A bridging point, the head of navigation, a sheltered harbour, or a strait everyone has to pass through.
• Centrality. Reachable from the whole territory, which matters more the larger and older the state is.
• Compromise. Nobody's first choice, and that's the qualification.
• Statement. A new capital declaring a break with the last one — a new republic, a new alignment, a new part of the country to develop.

The quickest tell for a purpose-built capital is the street plan. Organic capitals have a medieval tangle at the centre and rings of later growth around it, because they're what happens when a fort or a market spreads outwards for centuries. Planned ones have axes, symmetry, monumental sightlines and an obvious idea about where you're supposed to stand and look. Washington, Canberra, Brasília, New Delhi, Islamabad and Abuja are all legible from the air in a way that London simply isn't.

Egypt has been building a new administrative capital in the desert east of Cairo since 2015, for much the same reasons everyone else has done it — the old one is congested, expensive and hard to redesign. Whether the ministries and the embassies and everyone else follow is the question every one of these projects has had to answer, and the answer usually takes about thirty years.