Edo

Tokugawa Ieyasu arrived in 1590 at a minor castle on a bay full of reed beds. In 1603 he made it the seat of the shogunate, and for the next two and a half centuries Japan was governed from here while the emperor remained in Kyoto.

The policy that built the population

From 1635 the shogunate required every regional lord to spend alternate years in Edo and to leave his wife and heir here permanently. Sankin-kotai was designed as a control mechanism — a hostage system with a travel schedule — and its side effect was a city.

Hundreds of lords maintained Edo mansions with retinues. Feeding, clothing, housing and entertaining them required an enormous population of merchants and artisans. By around 1721 Edo held roughly a million people, likely the largest city on earth at the time.

The land split was brutal. Samurai households held the great majority of the ground; the townspeople — the chonin — were packed into a small fraction of it, at densities that made the fires inevitable.

Fires were so frequent that Edo called them "the flowers of Edo." The 1657 Meireki fire killed on the order of a hundred thousand people. The castle keep burned with them and was never rebuilt.

High city, low city

The geography split the culture. Yamanote — the "hand of the mountain," the western bluffs — held the samurai estates. Shitamachi — the "low town," the flats east toward the river — held the merchants, the craftsmen, the theatres and the fish.

That division is still legible. Shitamachi speech, Shitamachi humour and Shitamachi food are recognised categories in Japanese; Asakusa and Ryogoku are Shitamachi and feel it. The Yamanote Line, the loop you will ride, is named for the high ground it traces.

Then it was erased twice more

In 1868 Edo was renamed Tokyo, the eastern capital, and the emperor moved into the shogun's castle. The 1923 earthquake destroyed much of the low city, and the firebombing of 10 March 1945 killed something on the order of a hundred thousand people in a single night and flattened most of what was left.

So Tokyo has almost no old buildings. What it has instead is old shape: the spiral of moats around the palace, the position of the bridges, the boundary between high and low. Nihonbashi — the bridge of 1603, rebuilt in stone in 1911 — is still kilometre zero: every highway distance in Japan is measured from a marker at its centre. An expressway was built directly over it in 1964, and the city is now, slowly and at great expense, taking that expressway back down.