Pamplona is located in central Navarre in a rounded valley known as the Basin of Pamplona. Three rivers flow through the city, which borders France. The old town has a Roman origin and is organized around the Plaza del Castillo. Urban growth throughout history has led to densification. In the 19th and 20th centuries, the first expansions adopted an orthogonal plan. Pollution levels have increased, exceeding limits for CO2 and ozone and negatively impacting health. The government of Navarre is working to manage air pollution problems.