The London they established shared one feature with its latter-day descendant. It was highly cosmopolitan. North Africans, Italians, Spaniards, Germans thronged its streets. Here a certain Demetrius threw a silver plaque into the river imploring the river gods (in Greek) to save him from the plague. Here a child called Hector lost his shoe in the same river.
In London today, around 200 languages are spoken and there are followers of all the major religions. There are clues to this diverse pedigree in names such as Jewry Street and Greek Street; in buildings like the French Church of Soho Square or the Dutch Church in Austin Friars; in places like the old Sephardic burial place in the Mile End Road; in food (and the very word 'nosh' - a Yiddish one). Without migration there would have been no George Bernard Shaw in London, no V S Naipaul, no Joseph Korzeniowski (renamed 'Conrad'); no events like Notting Hill's Caribbean carnival.
But London's ethnic diversity has long been recognised, and even been put to work. Chinatown markets itself with oriental gates and phone booths that look like part of the set of Chu Chin Chow. Brick Lane and London Transport woo tourists with images of Asian swathes of colour. The marketing of ethnicity may have its uses (it saved Chinatown some years ago from demolition) but it also carries its dangers, bringing with it an impression of exoticism and top dressing. It reinforces the belief that immigrants somehow slotted themselves, under sufferance, into the interstices of an existing culture. In fact, they have been actively responsible for it.
As Nick Merriman and Rozina Visram firmly state in their introduction to this book of essays, London is and always has been an immigrant city - built by outsiders, and progressively changed and developed by outsiders. The Peopling of London singles out 17 different groups, including several vast catch-all categories - such as 'South Asians' - and ranging from the Huguenots (ancestors, it has been claimed, by blood or marriage, of 75 per cent of Londoners) to modern-day incomers like the Australians and Vietnamese. The essays focus on the reasons why people came, documenting the great forces of need and trade which have brought waves of new talents and skills regularly into London. Today's Southwark commemorates the presence years ago of Flemish weavers in its 'Weavers Lane'. The Stock Exchange was established, in its early form, by Dutch, Huguenot and Jewish financiers; ice-cream was introduced by Carlo Gatti in 1850. Upheavals and persecution brought in refugees from France (who gave the word to the English language), Eastern Europe, Russia and beyond. 'This town is more Irish than most of the places at home,' wrote Donall Mac Amhlaigh in 1957, from a community that is still the largest single immigrant group in London.
And so the story goes on, year in, year out. World events bring new people in, despite restrictions. Communities themselves, the authors show, change over time, and move about the city. The Cypriots can be traced along the route of the 29 bus; the Jews fanned out from the East End to Hendon and Ilford. Some assimilate into Britain; some resist assimilation; many others, the book stresses, are denied the chance. London may have been formed by immigrants, but this is not a parentage it is keen fully to admit.
The Peopling of London, with its poignant illustrations and accompanying exhibition at the Museum of London, attempts to establish the part immigrants have played in the creation of London. Without them, what would there be? Even the herds of reindeer have long moved on.