The 2600 years include both the rise of Rome as a superpower, from the 7th century BC to the early years of the 5th century AD, and the very gradual emergence of French as a distinct language, from the so-called "vulgar latin" spoken by the Roman soldiers to the homogeneous French language currently used.You have to bear in mind that a language evolves very slowly, with more rapid changes following "traumatic" events (invasions, revolutions, etc...). After Gaul was conquered by the Romans, the Celtic people who had long spoken Gaulish adopted the language of their victors. By then the Latin spoken by the legions was no longer classical Latin. However, to the vanquished, Latin (with its alphabet and literature) held a degree of prestige, and, for the surviving Gaulish élite, guaranteed quicker integration into the Roman world. Also, more profitable business. Apparently, pockets of spoken Gaulish survived well into the 6th century AD, but basically the Gallo-Romans spoke Latin. After the fall of Rome (ca 410 AD), "barbarian" tribes invaded and settled Gaul. They spoke Germanic languages, which coexisted for a while alongside with Latin. Little by little, though, the native Gallo-Romans being more numerous, their language prevailed. Latin was the language of clerks and scholars, and survived unchanged in that sphere, but as time went by, the illiterate commoners developed diverse local versions of a more and more simplified Latin, which became known as the Romance language(s). By the 10th century AD, the French languages that had emerged from Latin had retained only two grammatical cases, the "cas sujet" (nominative) and "cas régime" (accusative). A number of germanic words had entered the language. Latin and Romance were no longer mutually intelligible. The northern half of France, more densely settled by the Germanic-speaking Franks, developed the Langue d'Oïl (after their pronunciation of the word "oui"), while the southern half retained dialects closer to Latin (the Langue d'Oc dialects).There was no linguistic unity though. From valley to valley, the dialects changed ever so little, but if you went far enough, your dialect was not understood. This was true across the "Roman" world. From south Portugal all the way across Spain, then across France, then all the way down to Sicily, a dialect followed another, slightly different, but... different.Little by little, in France, a number a very charismatic kings (François 1er, Henri IV, Louis XIII, Louis XIV) managed to increasingly centralize the political power in Paris, defeating powerful but rebellious dukes. The Renaissance and the invention of the printed press ushered in a new era : the language spoken in Paris by the court became the norm. Official papers were written in that language all over the kingdom. The Siècle des Lumières (the 18C) then normalized the otherwise anarchic spelling. In the late 19C, compulsory education made French the one and only acceptable language. Dialects were banned from schools, and children punished when they used them. Over the 20C, most dialects went extinct, except for non-French outliers like Basque, Breton, Alsacian, and Corsican.I've got "family papers" dating back to the 1660s. They are in French, and fairly easy to decipher. Yet, my grandmother (died 1990) spoke dialect with her sister and neighbours). My parents were the first generation not to use dialect in everyday life.