Jakarta, a city of newcomers.

At the northern edge of Jakarta, along a pier almost two kilometres long, two-masted wooden sailing ships still tie up. They are called pinisi, they have been built for generations by the Bugis of South Sulawesi, and they still carry cement, timber and goods to the small ports of the archipelago. A few minutes away, the other scale begins: more than thirty million people in the metropolitan area, one of the largest urban concentrations on the planet. The two scenes seem to belong to different centuries, and in fact they tell the same story.

Jakarta began as a port and, in every way that matters, it never stopped being one. Not a port for ships: a port for people. Whoever looks here for an old town that explains everything, a "pure" local cuisine or an original people with centuries of unbroken continuity soon gets frustrated. Whoever understands that in this city the truly old thing is arriving itself begins to see the place clearly.

01 A port with four names

Few cities carry their biography in their name. This one was called Sunda Kelapa when it was the port of the Sundanese kingdom; Jayakarta — "complete victory" — from 1527, when forces of the Demak Sultanate took it; Batavia from 1619, when the Dutch East India Company razed it and rebuilt it in its own image, naming it after the Batavi, the tribe the Dutch regarded as their ancestors; and Jakarta since independence, in the mid-twentieth century, when it recovered a form of the old name. Four names, and each one marks the same event: the arrival of someone new with the power to rename it.

The revealing detail is that the first name is still alive — and still working. Sunda Kelapa is now the city's old port, and not as a stage set: the pinisi lined up along its pier are working cargo ships, linking Java with Borneo, Sulawesi and the smaller harbours a modern container vessel never reaches. In the age of the automated port of Tanjung Priok, wooden sailing ships still do, in plain sight of anyone who walks over, the work that founded this city five hundred years ago.

02 The natives who came from elsewhere

Seventeenth-century Batavia was a city where almost nobody was from Batavia. Dutch administrators, a large Chinese community, Malays, Javanese, Balinese, people from Ambon and Makassar — and, beneath them all, an enslaved population brought from across half a continent, at times more than half of the city's inhabitants. The Company sorted that mosaic by origin, in separate neighbourhoods for each community. Today's map still confesses it: Kampung Melayu, Kampung Bali, Kampung Ambon — "village of the Malays", "of the Balinese", "of the Ambonese" — remain the names of districts of the city.

Out of that forced coexistence, over the eighteenth and nineteenth centuries, something crystallised that no plan had foreseen: a new people. The Betawi — the name is the Malay pronunciation of "Batavia" — are the product of that mixture, and their language documents it word by word: a Malay-based creole with loanwords from Hokkien Chinese, Arabic, Portuguese and Dutch. Here is the discovery that reorders the whole city: the Betawi are considered Jakarta's original people, and yet they first appeared as an ethnic category in a census in 1930. The city's "natives" are four centuries younger than the city itself. In Jakarta, even being from here is a way of having come from elsewhere.

The stage where all of this happened survives in Kota Tua, the old town. On Fatahillah Square, the former city hall of Batavia — built in 1710 and modelled on Amsterdam's royal palace — presides over a flagstone esplanade that was once the administrative heart of the colony; along one side runs the Kali Besar, the canal that carried goods up from the harbour. It is a fragment of a Dutch city planted six degrees from the equator: the first visible layer of all the ones that came after.

03 A megacity made of villages

Kampung means village. In Jakarta it names something else: the dense, fine-grained neighbourhoods that live behind the avenues, home to the vast majority of the city — around eighty per cent of its residents, according to urban studies. They are not slums and they are not the exception: they are Jakarta's normal fabric, hundreds of urban villages wedged between towers, with alleys that hold at once the home, the workshop, the food stall and the entire life of a community that knows itself by name.

The city's administration takes that reality literally. Jakarta is divided into neighbourhood units called RT — a few dozen households in theory, often more than a hundred in practice — grouped into larger community units called RW. In other words: one of the largest urban agglomerations in the world is managed, at its finest scale, as thousands of adjoining villages, each with its own neighbourhood head and its own affairs. The newcomer who rents a room in a kampung does not join an abstract metropolis: they join one specific village, with neighbours who know who they are.

This is the tension that defines the physical experience of Jakarta: it is simultaneously one of the biggest cities on Earth and one of the smallest. From an elevated walkway downtown you see the skyline of towers; three streets back, someone is watering the plants in an alley two metres wide where everyone greets everyone. The two cities do not take turns: they are interlocked, block by block.

04 A culture that shows its seams

Many urban cultures disguise what they have borrowed. Betawi culture does the opposite: it puts it on display. Its most visible figures are the ondel-ondel, puppets up to three metres tall that are paraded through the streets at celebrations, born of the same mixture as everything else — scholars trace Sundanese, Javanese, Malay, Chinese and European influences layered inside them.

The local music is even more explicit. Jakarta's "traditional" band is called tanjidor: trumpets, trombones, clarinets and European marching percussion. The name itself comes from the Portuguese tangedor, "one who plays", and the genre descends from the musicians of the colonial era who kept playing the European military-band repertoire on their own account after Batavia abolished slavery in 1853. In Tugu, in the city's north, the community descended from the Portuguese-speaking Mardijkers preserves keroncong, a music of guitars and ukuleles with Lusitanian roots. Jakarta's most local tradition sounds like instruments from other continents, and nobody thinks of hiding it: that, exactly, is the tradition.

05 The city that lends its voice

For centuries, Jakarta absorbed the archipelago. Now the reverse also happens. The colloquial Indonesian spoken from Sumatra to Papua — bahasa gaul, the informal language of television, social media and the street — is built on Jakarta's Betawi speech, spread by the national media until it became the standard way to talk casually across the country. The slang born in the alleys of a city of immigrants is today the informal voice of a nation of more than 17,000 islands. The port that spent centuries receiving the archipelago gives it back as a language.

And once a year the city reveals its nature all at once. Around the Lebaran holidays, Indonesia's great national break, comes the mudik: the mass return to hometowns. Millions of people leave Greater Jakarta within days — in recent years, more than twenty million — and the megacity falls quiet. It is the most honest census there is: almost everyone here has another home somewhere else. As early as 1961, at the height of the urban boom, barely half of the city's inhabitants had been born in it; today Jakarta's largest ethnic group is not the Betawi but the Javanese. The statistics confirm what the mudik acts out: this is a city of people who came.

06 What stays

At the geometric centre of all this lies an outsized square: Merdeka Square, some eighty hectares of lawns and avenues around the Monas, the 132-metre obelisk crowned with a flame covered in gold leaf. From its viewing deck the city stretches in every direction with no visible edge. It is a good place to think about the latest move in this story: the state has begun transferring administrative functions to a new capital in Borneo. One suspects it will affect Jakarta less than it seems: this was a port before it was a capital, and what sustains it is not an administrative title but five hundred years of the habit of receiving people.

What stays in the memory after a few days in Jakarta is rarely a monument. It is a feeling that is harder to name: that of a city where arriving from elsewhere does not make you a foreigner, because arriving from elsewhere is what founded it, what populated it and what keeps making it grow. The pinisi loading at the old pier, the village names on the map of the megacity, the language of its alleys spoken across an entire country. Some places are defined by what they preserve. Jakarta is defined by what it receives.