Despite the name, this is not a palace. It's an extravagant monument to the glory of water and its crucial importance ever since Marseille was founded by the Greeks in 600 BC.
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With an average of only two days of rain a month in the midsummer, drought has always been a problem for the region: this is, of course, the central theme of Marcel Pagnol's famous stories, Jean de Florette and Manon des Sources.
A series of cholera epidemics finally prompted the authorities in 1834 to commission a canal linking the city to the river Durance.
The aim was not only to create a water source. The canal would connect Marseille to the national waterway network and open up new trading routes. That was urgently needed following France's invasion of Algiers in 1830 and its other colonial activities in the Maghreb.
80 km / 50 miles long, including 17 km / 10.5 miles of underground tunnels, the canal took 15 years to build and required 18 aqueducts. It was opened in 1849, and remained Marseille's principal source of water until 1970, clearing the way for the city's economic growth and prosperity.
Something was required to celebrate its completion, and so the Palais Longchamp was born. Designed by Henri-Jacques Espérandieu, the architect of Notre Dame de la Garde, it was inaugurated in 1869.
It's a stupendously large and elaborate monument: a sort of mix of fountain, waterfall and water tower, all rolled into one.
Of a positively Parisian opulence, it's embellished with colonnades, staircases, pavilions and a triumphal arch and lavishly decorated with sculptures of nymphs, stalactites, lions, tigers, dolphins and Camargue bulls like the one pictured.
Located in a quiet residential suburb east of Saint Charles Station, the Palais Longchamp is surrounded by spacious grounds traversed by the final part of the canal along an aqueduct. Apart from the green space in front of the monument, there are three big, interconnected parks behind it.
One of these was a zoo in the 19th century, and you can still see many of its picturesque buildings in fantastic styles. Among them are pavilions for giraffes and elephants, cages ornamented with Turkish tiles, and seal dens decorated with rocaille (rock-work). Pictured, this oriental giraffe house has now been converted into a little children's theatre.
In 2013 as part of the Marseille-Provence European City of Culture programme, this part of the Palais Longchamp's grounds was repopulated with whimsical, brightly-coloured fibreglass animals to form a "Funny Zoo". Some of these animals remain in place today, even if they're not terribly well maintained.
The Palais Longchamp and its park boast ancient trees, fine views across Marseille (Notre Dame de la Garde can be glimpsed in the distance, plentiful places to picnic and several children's playgrounds.
It all makes for an attractive, restful excursion on a summer's day to escape the heat of a city not famed for its squares, parks and leafy spaces. Click here to read about things to do for families with children at the Palais Longchamp.
In July, the huge park at the Palais Longchamp is the main venue for the prestigious annual Marseille Jazz des Cinq Continents festival, though the event is now increasingly spilling over to other venues as well.
In 2016 the Marseille Jazz Festival acquired a new Artistic Director, the jazz pianist Stéphane Kochoyan. Among the artists invited were Ibrahim Maalouf, Didier Lockwood and Jan Garbarek. In 2017 it runs from 19-28 July.
Tickets to the top acts at the Jazz Festival can be pricey: as much as 50 €uros. Visit the park instead in the afternoon, when the artists can be heard rehearsing - and admission is free. The opening night sometimes features a free concert too.
Also of interest are the museums occupying the Palais's two wings, the Museum of Natural History and the Museum of Fine Art. The former has four sections, devoted to prehistory and evolution, osteology (that's skeletons and skulls to you), the flora and fauna of Provence and a "safari room" featuring over 300 exotic (stuffed) animals. It also hosts temporary exhibitions: the current one explores our sense of smell. Until 30 April.
Recently refurbished, the latter reopened to the public in 2013. It has a large permanent collection of European and, specifically, provençal art from the 16th to 19th centuries.
In the park behind the Palais are a small observatory, with a planetarium (pictured), temporary exhibitions and Foucault's enormous historic telescope - once the largest in the world - dating from 1864.
Across the road is the Grobet-Labadié Museum, which recreates the intimate and comfortable atmosphere of a wealthy 19th merchant's house, with tapestries, wood-carvings, musical instruments, chinaware and paintings; even a sedan chair.
Where: Palais Longchamp, Boulevard du Jardin Zoologique, 13004 Marseille.
How to get there: Metro line 1 (stop: Cinq Avenues Longchamp), tram line 2 or bus 81.