The course of the road has been reconstructed from the writings of Herodotus, archeological research, and other historical records. It began in Sardis near the Aegean coast of Lydia, traveled east through Anatolia (crossing the Halys according to Herodotus), and passed through the Cilician Gates to the old Assyrian capital Nineveh in upper Mesopotamia, then turned south to Babylon. From near Babylon, it is believed to have split into two routes, one traveling northeast then east through Ecbatana and on along the Silk Road (via the Great Khurasan Road), the other continuing east through the future Persian capital Susa and then southeast to Persepolis in the Zagros Mountains. Of course, such long routes for travellers and tradesmen would often take months on end, and during the reign of Darius the Great numerous royal outposts (Caravanserai) were built.