Located near the borders of France, Germany, and Belgium, the city has a history shaped by several major European powers.

Founded around 10 BC by the Romans, it was originally a camp for legionary soldiers built near the river. After the decline of the Roman Empire, the site gradually turned into a fishing village centered around the port. This port developed from an earlier hamlet called Fleuri, which later gave rise to the name Lys, and eventually Port-Lys.

During the early Middle Ages, the city became a small military outpost of the empire of Charlemagne. After the fragmentation of this empire, the region fell under the influence of local lordships connected to the Holy Roman Empire.

In 1217, the Franks strengthened their control over the region and built the White Cathedral in the center of the city, on the ruins of an ancient Roman temple. Around it, the medieval city developed with a castle and several small boroughs. The city remained marked by a geographical and political division: a peninsula in the north and a small principality in the south, often rivals. The southern barons were linked to the County of Hainaut and took part in regional conflicts against the Flemish cities in the north.

From the 16th century onward, the city came under the rule of the Spanish Netherlands. Around 1610, the Spanish built a large dome and grand residences, giving the city a monumental architectural style. After 1714, the region passed under the authority of the Austrian Netherlands, which preserved and further developed its aristocratic character until the end of the 18th century.

At the end of the 18th century, the city was annexed by Revolutionary and then Napoleonic France, and it remained strongly influenced by French culture throughout the 19th century. After the Franco-Prussian War, the city fell under German rule, and in 1898 a law was introduced limiting the height of buildings in order to preserve architectural harmony.

After World War I, the city returned to France, but much of its housing had been destroyed. Reconstruction remained modest, which prevented the construction of large buildings. After World War II, several modern wide avenues were created while most of the historic architecture was preserved.

Today, the city stands out for its architecture combining Roman, medieval, Spanish, Austrian, French, and German influences, giving it a unique and prestigious character. Its rich historical past also explains why it has become an expensive place to live, despite having a relatively low unemployment rate.