Frankfurt, located in the foreland of the Taunus on its namesake Main, it forms a continuous conurbation with the neighboring city of Offenbach am Main. Frankfurt was a city state, the Free City of Frankfurt, for nearly five centuries, and was one of the most important cities of the Holy Roman Empire, as a site of Imperial coronations. Frankfurt is a global hub for commerce, culture, education, tourism and transportation, and is the site of many global and European corporate headquarters. The city has many notable green areas and parks, including the Wallanlagen, Volkspark Niddatal, Grüneburgpark, the City Forest, two major botanical gardens (the Palmengarten and the Botanical Garden Frankfurt) and the Frankfurt Zoo.