The capital city of Belgium has several synonyms that are commonly used. The most popular synonym is Brussels, which is the official name of the city and is widely recognized as the capital of Belgium. Other synonyms include Bruxelles, the French name for the city, and Brussel, the Dutch name. Additionally, the city is sometimes referred to as the European capital, as it is home to the headquarters of the European Union and NATO. The city is also known for its historic and cultural significance, and is often referred to as the capital of art nouveau architecture due to its abundance of art nouveau buildings.