Located near the Metro station Strasbourg-Saint-Denis (specifically at the intersection of Rue Saint-Denis and Boulevard Saint-Denis/Boulevard de Bonne Nouvelle), the monument is actually not considered one of Paris’s “arcs,” but instead is designated as a “porte (gate)” since it served as an entry point into the City of Light through one-time fortifications that surrounded Paris.
The fortification was known as the Wall of Charles V and was built from 1356 to 1383 to protect the Right Bank of the city. It was eventually partly torn down in the 1640s to make way for the larger, more fortified Louis XIII Wall and then was entirely demolished in the 1670s when Paris spread beyond its confines.
At nearly 25 meters in height (about 82 feet tall) and the same width, the arch commemorates the military victories of King Louis XIV, specifically over Germanic groups long the Rhine River. Those victories established what essentially still serves as the border between France and Germany today.
The structure includes one large central arch and two smaller square doorways to either side that once served as pedestrian-only portals but have been sealed since the arch was completely renovated in 1988. The north face of the arch includes sculptures of allegorical figures of the Rhine and the Netherlands, while the south facade has a relief by sculptor Michel Anguier titled “The Passage of the Rhine” that focuses specifically on France’s military successes in the region.
A similar but smaller arch, the Porte Sainte-Martin, is located about three blocks east of the Porte Saint-Denis. It, too, marks a former gate through the ancient fortifications around Paris.
Both arches are perfectly safe to visit day or night, but it’s important to note that the Rue Saint-Denis—which bisects the Porte de Saint-Denis running north-south—is notorious for housing numerous adult bookstores and porno palaces. While certainly seedy, they oddly blend in fairly seamlessly with the street’s numerous other shops and eateries so as to not create an unpleasant or unsafe atmosphere. (The same actually goes for Paris’s Pigalle district, which is well-known for its adult establishments but is also surprisingly clean, safe and accessible.)
The only downside can be heading up the Rue Saint-Denis just south of the arch (particularly at the corner of Rue Saint-Denis and Rue d’Aboukir) in the evening or at night: The area is thronged by female prostitutes, many of whom can be quite brazen toward potential male clients, especially if you make eye contact. The best advice is to simply offer a “non, merci” and keep walking if approached or addressed by any of the working girls; they’ll quickly turn their attention toward others who may be more interested.
Or, better yet, just skip the Rue Saint-Denis entirely and access the Porte from the adjacent Metro station or by walking along the Boulevard Saint-Martin/Boulevard Saint-Denis/Boulevard de Bonne Nouvelle (the same has three different names within just a five-block stretch). You won’t be missing much.