Walloon, the language of Wallonia

This is a good overall history of the language. It explains the four main dialects, the origins of the language from the first century BC in Gaul to present.

Some snippets/ time lines:
The story begins in the 1st century BC , in Gaul. The south-east has been a Romance province since 116. The population speaks a Celtic language, Gaulish, that probably comprises many dialects.
The romanization starts after Caesar's military campaigns.
Around the 4th century AD, Gaulish is reduced to a substratum..
13th century marks Walloon's clear recognition..
1600 marks the end of the Old Walloon period..
At the beginning of the 19th century, Walloon speakers began to raise the alarm when they noticed the decline of the dialect under the pressure of French.
Functioning and consequences of French-Walloon bilingualism