Basel (/ ˈ b ɑː z əl /, BAH-zəl; German: ⓘ), also known as Basle, [note 1] is a city in northwestern Switzerland on the River Rhine (at the transition from the High to the Upper Rhine). [4] Basel is Switzerland's third-most-populous city (after Zurich and Geneva), with 177,595 inhabitants within the city municipality limits. [5] The official language of Basel is Swiss Standard German ...