The Romans had begun their conquest of southern Gaul (later known as the Provincia) in 125 BCE.
Moving westward, they had founded in 118 BCE the colony of Narbo Martius (Narbonne), the Mediterranean city nearest to inland Tolosa, and thus have come into contact with the Tolosates, famous for their wealth and the key position of their capital for trade with the Atlantic.
Archaeological evidence dates human settlement in Toulouse to the eighth century BCE.
The location is very advantageous, at a place where the Garonne River bends westward toward the Atlantic Ocean and can be crossed easily.
It is a focal point for trade between the Pyrenees, the Mediterranean and the Atlantic Immediately north of these hills is a large plain suitable for agriculture.
People gather on the hills overlooking the river, south of the plain, nine kilometers south of today's downtown Toulouse.
The name of the city is Tolosa.
Researchers today agree that the name is probably Aquitanian, related to the old Basque language, but the meaning is unknown.
The name of the city has remained almost unchanged over centuries despite Celtic, Roman and Germanic invasions, which is rare for French cities.
The first inhabitants seem to have been Aquitanians, of whom little is known.
Later came Iberians from the south, who, like the Aquitanians, were non-Indo-European people.
In the third century BCE, there came a Celtic Gallic tribe called the Volcae Tectosages from Belgium or southern Germany, the first Indo-European people to appear in the region.
They settled in Tolosa and interbred with the local people.
Their Gaulish language became predominant.
Tolosa is attested by 200 BCE to be the capital of the Volcae Tectosages (based on coins found), which Julius Caesar will later call Tolosates in his famous account of the Gallic wars (De Bello Gallico, 1.10), singular Tolosas.
Archeologists say Tolosa was one of the most important cities in Gaul, and certainly it was famed in pre-Roman times for being the wealthiest one.
There are many gold and silver mines nearby, and the offerings to the holy shrines and temples in Tolosa have accumulated a tremendous wealth in the city.
Another consul, Quintus Servilius Caepio, marches to Gaul in 106 BCE and plunders the temples of Tolosa, finding a huge sum of money: over fifty thousand fifteen-pound bars of gold and ten thousand fifteen-pound bars of silver.
Strabo reports a story told in his time of this semi-legendary treasure, the aurum Tolosanum, supposed to have been the "cursed gold" looted during the sack of Delphi during the Gallic invasion of the Balkans in 279 BCE.
The riches of Tolosa are shipped back to Rome via Massilia, but only the silver arrives; the gold is stolen by a band of marauders, who are believed to have been hired by Caepio himself.
The Gold of Tolosa will never be found, and is said to have been passed all the way down to the last heir of the Servilii Caepiones, Marcus Junius Brutus, the famous assassin of Julius Caesar.
Tolosa chooses to ally with the daunting Romans, who in 106 establish a military fort in the plain north of the city, a key position near the border of independent Aquitania, but otherwise leave the inhabitants free to rule themselves in semi-independence.