Marseilles is a city that only really opened up to tourism at the very end of the twentieth century.
Marseille is the "oldest city in France" and indeed one of the oldest in western Europe. The city was founded as Massalia in around 600 BC, and soon developed into an important port in the ancient Greek world. For the Greeks, and later for the Romans, it was a major point of transition and trade between the civilisations of the Mediterranean, and those of Gaul and northwest Europe.
And that, essentially, has been Marseilles' role ever since. Located near the mouth of the Rhone - the greatest natural corridor between the Mediterranean and the lands to the north, it has long been one of the most important, when not the most important, port in France – a role that explains its importance and its size, as France's third largest urban area, to this day.
Rather in the same way as Genoa or Naples, Marseilles' importance as a port rather hindered its development as a tourist destination; and while other Mediterranean ports like Barcelona and Valencia began to develop their tourism in the 1970's, Marseilles did not. Its port was too important. But more recently, Marseilles has managed maintain its status as one of the most important ports on the Mediterranean, and develop as a tourist destination at the same time.
The paradox with Marseille is that although it stands proudly beside the Mediterranean, it is not a seaside resort. The gentler and flatter coast northwest of the city is occupied by the docks, and southwards from the "Old Port", the seashore is rocky, with no beaches until the Plage du Prado, 6 km further south. So it's not a place to visit if the aim of the trip is solely or mainly to enjoy the beach. The shoreline and the waterside ambiance, yes; but the beach, no.
For a day-trip or a weekend break or short stay, Marseilles is an ideal destination, specially during those times of the year when it tends to be bathed in Mediterranean sunshine while much of France further north is still struggling with spring or dampened by autumn mists and showers. And getting to the tourist quarter of Marseille around the Old Port is remarkably easy.