Author of books on superweapons, Albert Einstein, and science in German literature. His latest – City: A Guidebook for the Urban Age – is published by Bloomsbury.

It’s beautiful isn’t it? Just like I knew it would be,’ says Dorothy in The Wizard of Oz, as she catches her first glimpse of the sky-high crystalline towers and domes of the Emerald City glittering on the horizon. In this fairy-tale film from 1939, Dorothy expresses the feelings of millions of people arriving for the first time in real cities around the world, all of them hoping and praying that this will be the city in which their dreams are finally realised.

We freight our cities with impossible expectations. Throughout history, architects and urban visionaries have played upon these hopes to conjure up beguiling visions of a shining city on a hill, a eutopia whose very buildings and spaces instill a sense of order and fulfilment in their inhabitants. Such ideal cities teach you the good life with every step taken upon their pristine pavements. Of course, the reality of urban life has generally fallen far short of such lofty ideals.

Just as my book City, which is designed as a guidebook to an imaginary ‘Everycity’, uses examples from the past, present and future of urban life to tell the global story of the city, so my kind of town is a composite, built from those aspects of cities that have most impressed me.

London is the city I know best. I grew up in its unlovely suburbs, in a 1930s Romford semi. Later I was fortunate enough to study (and then teach) in one of the city’s most beautiful areas: Bloomsbury. Sigfried Giedion has said it is an architectural composition the equal of St Peter’s Square in Rome. I agree. Its garden squares form green islands of tranquility amidst the clamour of the modern city. One of my favourites is Russell Square Gardens, a regular way station for me en route to the area’s research libraries. With its green spaces and elegant terraces designed on an impeccably human scale, Bloomsbury is one of my favourite districts in any city.

My ideal city would not be a new town. History is important to me. I like cities in which you can travel through time. Go to the twelfth-century basilica of San Clemente in Rome, a few minutes’ walk from the Colosseum. In an annex now used as a souvenir shop there is an unremarkable wooden door which opens onto a flight of stone steps leading down under the church. They take you back some 1,600 years. The church stands on top of a much earlier one. You can walk down its nave and admire the beautifully fluid frescos on its walls. But beneath it lie yet more layers of Rome’s history. For underneath both of these churches, you can walk on the streets of first century Rome. There is even a pagan shrine, a temple to Mithras, a god of wisdom and light. Standing in front of this ancient temple, many metres below street level, with the roar of an underground river in your ears, the city’s past and the lives of its people are made powerfully present.

By the third century AD, Rome was the biggest city in the world, home to more than one million people. Today’s most populous megacity is Tokyo. Despite its size – as many live there as in the whole of Canada – it is one of the friendliest cities I have visited. If you stop in the street to look at a map, before long someone will try to help you. It is also the cleanest and most efficient city I know. Its public transport system is the envy of every metropolis. But spotless streets and trains that run on time don’t make a truly great city. Cities are far more than the sum of their infrastructure. A city is made great by its people. The most creative and dynamic cities are often those with the most diverse populations. From Renaissance Venice to modern New York (which has some 170 immigrant groups), successful cities have always thronged with people and goods from far-off lands. They bring with them unique vocabularies and street foods – New York’s German immigrants created hot dogs and hamburgers – as well as new ideas. With a thriving economy, a city like this can become one of the most exciting and exhilarating places on the planet.

The garden squares of Bloomsbury, the evocative history of Rome, the friendliness and efficiency of Tokyo and the dynamic diversity of New York City – these would all form vital aspects of my ideal city. Oh, and it would have great cafes, too – somewhere to sit and watch the street life of this extraordinary place.

First published in AT229, June 2012