Le Corbusier's pioneering urban housing experiment is known poetically as the Radiant City, prosaically as the Unité d'Habitation and irreverently by locals as La Maison du Fada (The Madman's House).
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Whatever you call it, this is much more than just another block of flats. The building is a miniature self-contained town in its own right. The corridors on each floor are even known as "streets"!
It incorporates a pâtisserie, other shops and galleries, a primary school, roof terrace and other facilities, all set in 4 hectares / 9.8 acres of parklands, also landscaped by Le Corbusier.
The scope of the concept still remains remarkable today. Back in the bleak post-war years, when the Radiant City was conceived and built, it was simply revolutionary.
Retrospectives of Le Corbusier's work in galleries around the world often show his vision preserved as a museum piece. Here in Marseille is a chance to see it in living, breathing action. The Radiant City is fully inhabited. But it remains open to the public.
It was officially named a UNESCO World Heritage Site in 2016. The award was given to a "package" of 17 of Le Corbusier's greatest architectural works from all over the world.
Pictured, Charles-Edouard Jeanneret-Gris was born in Switzerland in 1887. But his heart was, as he says, profoundly Mediterranean: he died at his cabanon, or beach house, on the Côte d'Azur in 1965.
He took the pseudonym Le Corbusier - adapted from his grandfather's name, Lecorbésier, and meaning, roughly "the crow-like one" - in 1920.
Over the years, Le Corbu - as he's often known - turned his hand to very many things: painting, sculpting, furniture designing and, above all, urban planning.
Published in 1935, La Cité Radieuse (The Radiant City) articulated his radical ideas. Click here to read a review of the major exhibition spotlighting Le Corbu's work in a wide range of media which was held in in Marseille in 2013.
In some circles, Le Corbusier has a lot to answer for. He aimed to provide better living conditions in overcrowded cities. But many people regarded his huge monoliths as paving the way for the shoddy tower blocks that blighted British and American cities in the 1960s.
Built between 1947 and 1952, Marseille's Radiant City is in an altogether different class. Designed to a very high standard, it was originally conceived as social housing but today is a fashionable middle-class Mecca.
A handful of loyal residents have lived there since 1952. Other apartments come up for short-term lets or sale occasionally and are much sought after.
There was both insufficient steel and a shortage of skilled labour in post-war France. So, making the best of the situation, Le Corbusier conceived the structure in raw concrete, raised off the ground by large piloti or "stilts", pictured.
The concept, apparently stark at first sight, is embellished with a wealth of subtle detail. The spacious entrance hall has such touches as stained-glass windows and shell designs in the concrete walls.
On the upper floors, the "streets" are much wider than corridors in the average hotel or apartment block, where architects try to keep the maximum space for the private living quarters.
For Le Corbusier, the public areas are just as important. With their atmospheric lighting and richly coloured front doors the residential "streets" are an inviting place in their own right.
The unusual layout is intended to make maximum use of minimal space. 337 apartments are arranged over twelve storeys, interlocking, jigsaw-like.
Those on one side of the central corridors are entered at a single-aspect lower floor before ascending up to a double-aspect upper one (as in the plan below). Those leading off from the other side open into single-aspect upper floors before descending to double-aspect lower ones.
Every flat has a double-height reception room with mezzanine and a deep balcony.
And they all stretch from one side of the building to the other, looking east towards the hills on one side and west towards the sea on the other. Twenty-three different layouts provide living space for between one and ten people.
It's now possible to see inside several of the apartments at the Radiant City.
Apartment no.643 is officially listed as an Historical Monument because it remains almost perfectly preserved in its original state. It can be visited on one of the regular guided tours in English or French organised by the Marseille Tourist Office.
When we had a sneak preview of it in 2013, shortly before it opened to the public for the first time, the apartment was empty of furniture and still in the throes of redecoration, with colour samples of paint all over the walls.
It will no doubt look rather different now. Still, we got a powerful sense of the sheer brilliance of its interior design and the extent to which the ideas in it were way ahead of their time.
Even though it's one of the larger apartment in the complex, no.643 isn't huge. But every surface and spare corner has been used efficiently and ingeniously.
On the entry-level floor is a fitted kitchen, pictured, with service and delivery hatches opening to the dining area and outer corridor respectively.
It boasts an compact array of built-in units and appliances (there's an ice cupboard rather than a fridge). The blue swing door you can see in the photograph marks it off as a separate space.
The living area opens on to a loggia, with a concrete sun-screen, Le Corbusier's trademark primary-coloured walls and surfaces decorated with bright ceramic insets. The large, stylish door handle is perfectly ergonomic and the heating ducts are neatly concealed under the step to the balcony.
A staircase, pictured, leads to the upper level. Note the clever idea of two hand-rails, one at adult height and one for small children.
Le Corbusier designed a "Modulor" or gauge to calculate the optimum dimensions for each aspect of everyday living, geared to the size of the average human. A replica of this grid can be seen on the third floor of the Radiant City.
Upstairs at no.643 are two long narrow bedrooms for children, each with its own washbasin.
They're linked by a sliding door covered in a slate for the kids to draw on and share a single bright yellow ship's-style shower cabin. At the other end of this level is the large master-bedroom with en-suite bathroom and separate WC.
In the course of this fascinating visit, the guide will also take you around the entrance hall, the commercial "street" on the third floor and the roof terrace. You can book a tour of the Radiant City here.
For one month in the summer between mid-July and mid-August, the owner of one of the other apartments, no.50, opens this flat to the public after having invited a designer to redecorate it in his or her own individual manner.
They have included Britain's Jasper Morrison (2008), France's Ronan and Erwan Bouroullec (2010) and Germany's Konstantin Grcic (2013), who decked out the apartment in neo-punk style, with posters of Sid Vicious. Each designer nominates his or her own successor for the following year.
In 2014 the Apartment 50 was decorated by the French designer Pierre Charpin, who chose students from the Swiss university ÉCAL to refit the apartment in 2015, while Alessandro Mendini was the guest in 2016. Website for Apartment 50
You can also wander round the Radiant City on your own, though you won't be able to see inside an apartment. The residents are justifiably keen to preserve their privacy, and so individual tourists are requested to check in with the concierge in the entrance hall and to confine their visit to certain areas: the lobby, the third and fourth floors and the public part of the roof terrace.
On the third and fourth floors are rows of shops which were initially designed to cater to all the residents' needs and to make the Radiant City a totally self-contained community.
Facing competition from the nearby supermarkets, the food shops gradually moved out and today only a bakery remains (its owner has been there since 1969). The other commercial units are now occupied by galleries, bookshops and estate agencies.
Also on the third floor is the Hotel Le Corbusier, which offers small but perfectly formed rooms in Le Corbu style. Originally intended for friends and family visiting the residents, it's now open to everyone. The Radiant City's proximity to the Vélodrome makes it a good bet for Olympique de Marseille fans.
Next to it is a gastronomic restaurant, Le Ventre de l'Architecte, decorated in 1950s retro-chic in Le Corbusier's original spirit.
Originally designed as a gymnasium, the roof is a huge 600 square metre / 6,460 square foot terrace, pictured, with sculpted ventilation stacks, a paddling pool, an open-air performance space and sensational panoramic views.
It was purchased in 2010 and restored by the cult Marseille-born designer Ito Morabito, also known as Ora Ïto. He reopened an indoor space there in 2013 as an exhibition venue and bookshop.
There is - sometimes, when a show is on - a small entrance charge to enter the gallery but access to the open-air terrace, where artworks are also displayed, is free. Ïto calls the terrace MAMO, short for Marseille Modular.
The guest artist at MAMO in the summer of 2016 was the Swiss artist Felice Varini with A Ciel Ouvert, a display of three installations exploring perspective.
In 2015 the featured artist was the New Yorker Dan Graham with an exhibition of installations called Observatory / Playground.
The 2014 summer show was Défini, fini, infini and featured seven brand-new works by the French conceptual artist Daniel Buren. In summer, evening events are also held on the roof terrace featuring artists such as David Walters or Arthur H. Website for MAMO
How to get there: Metro line 2 (stop: Rond-Point du Prado). Then bus 21 or a 15-20 minute walk.
Find further reading on Amazon:
Le Corbusier: L'Unitae d'Habitation de Marseille (Corbusier Guides) by Jacques Sbriglio.
Towards a New Architecture by Le Corbusier.
Le Corbusier, Unite D'habitation, Marseille by Alban Janson, Carsten Krohn.