This article renegotiates the dilemma between modernist and primordialist views on nationalism by taking a long-term case: language and identity politics in the diglossic area between Liège and Maastricht. Linguistic assertiveness in this area (a nationalist flashpoint in 20th-century Belgium) can be traced back to the 15th century. While this long-term historical continuity indicates limits to modernist constructivism, it also illustrates the dangers of primordialism.