There are, of course, many histories of Arles ranging from the serious and scholastic to the wildly fanciful. Even the increasingly less unreliable Wikipedia has some good stuff and I would advise you to read at least some of it before you come. The following is by way of offering a few salient points only.
The area around what is now Arles has been inhabited for more than three thousand years and owes its prominence primarily to the River Rhône that rises in the Swiss Alps near Geneva and travels for some five hundred miles down through the middle of France before issuing into the Mediterranean. The river has always provided the main route for water-born trade from the Mediterranean into the heart of France as it is navigable to beyond Lyon some 300 miles inland and settlements were founded as early as 800 BC to provide trading posts and ship building and repair businesses in Arles, Avignon, Valence, Vienne and Lyon itself. Towards the end of the first millennium BC it was therefore adopted by the invading Romans to provide a major staging post. The relatively flat land to the east of what is now the city, the so-called Plan de Crau, was a very fertile area for agriculture while the delta that had formed between the Grand and Petit Rhone rivers after the river splits just north of the town was similarly fertile and also provided grassland suitable for growing corn and the raising of beef cattle - the area now know as the Camargue.
The river also provided a second reason for Arles rise to prominence at the turn of the first millennium AD and that was that it was the point where the great river turns sharply west, (heading downstream) almost at right angles to its previous long southerly course, narrowing enough in the process to provide the first real opportunity to construct a bridge and thus help complete the part of the great Via Aurelia that was created by the Romans around the turn of the first millennium AD to provide a land route from Rome into Spain. The river carries a huge amount of water, especially during the spring when the snow is melting further north, and the river stream around the corner can be very fierce indeed and, over time, successions of pontoon bridges strung across the narrowest point were regularly destroyed either by the water or by ice carried down the river. The great bend also meant that, throughout its history, the low south bank allowed the river to flood the town also on a regular basis. In spite of numerous and extensive engineering activities to control this, it has been know to happen in modern times as well as ancient ones. The most recent serious inundation was in 2003 although there is evidence (much debated, of course) that the severity was greatly increased by human error in the management of the water engineering further up-stream. The flow was measured in Beaucaire at a record thirteen thousand cubic metres per second which is, I am told, a lot.
Arles was clever - or lucky - enough to side with Julius Caesar in his disagreement with Pompey in 49BC, the latter being supported by Massalia (Marseille). Caesar’s triumph saw a lot of Marseille’s wealth transferred to Arles and when it was decided to house a major veteran’s legion in the town, Arlelate (Arles) was set for a prosperity that lasted for some five centuries. Most of the great Roman building in the town dates for the first century AD.
After another five hundred years when Arles’ affluence waned as it was continually fought over, it came back briefly into prominence in the 12th century when Frederick Barbarossa came to Arles for his coronation as Holy Roman Emperor in 1178 but its influence and prosperity again declined thereafter although it was to some extent kept alive by the river and the trade in goods and shipping services it provided.
The most recent and possibly last economic renaissance for the town started in 1846 with the establishment of a large railway factory in the Alyscamps area to the south-east of the town centre to service the new line between Avignon and Marseille. While its precise function changed throughout the nineteenth and twentieth centuries, it remained as a major employer for the local population and was the last great engine of prosperity for the town. The town’s reliance on its river was, however, finally broken just as the new method of transportation for people and goods eclipsed the old water-born industry.
There have been a few famous sons and daughters of Arles over the years. The Nobel prize-winning poet Fredrick Mistral invested much of his prize in the preservation of the Occitan language. Van Gogh, although not a native, lived in the town for eighteen months in 1889 and painted some of his most famous paintings there. His friend Gauguin stayed less long. More recently, the photographer Lucien Clergue and the fashion designer Christan Lacroix have joined Arles small roll of honour, as have a few notable footballers and bull fighters. Arles was also home to Madame Calmet who at the time she died in 1997 was the oldest documented human on the planet at one hundred and twenty two and a half.
During the Second World War the plant was taken over as a service depot by the occupying German army (the whole French railway system was commandeered) and there is some evidence to suggest that it became a significant centre for resistance to the occupation - one of the few real ones in the region in spite of more “modern” versions of French domestic history in which every French town and village has been re-discovered as a hotbed of anti-Nazi resistance. After the war some attempt was made to keep it going as a specialist engineering facility but it soon fell into disrepair until very recently when a number of attempts have been planned to make use of the site and its buildings as some sort of enormous cultural centre. Time will tell whether these efforts bring any actual prosperity to the town rather than just cultural window-dressing for visiting tourists. Opinions amongst most detached observers are divided. To this day Arles remains a very poor town with a high level of unemployment and social deprivation. The town relies on tourism. There are few significant employers in the town and, other than tourism, agriculture is its only major source of income.