Join オンライン upcoming events being held in Rosetta. Rosetta is a historic city in Egypt, located at the mouth of the Nile River, known for its well-preserved 15th-century fortress, beautiful Islamic architecture, and as the site of the discovery of the Rosetta Stone, a slab of black basalt inscribed with three versions of a decree issued in Memphis, Egypt in 196 BC, which provided the key to deciphering Egyptian hieroglyphs.