To the north of Pars, the province Parthau consisted essentially of the drainage area of the Zanda river, from the mountains of the Bakhtiyari tribes on the Khuzistan border to the neighboring cities of Aspadana (Spahan, Isfahan) and Gabe (Gay, Jay). In the east this region, known to Strabo as Paraetacene (xv.2.14, 3.12), bordered on Kirman. It may have included Isatichae (Yazd); or else the latter city, in agreement with Ptolemy, may have been the most westerly major city of Kirman. Its western mountains adjoined those of Mah, the country of the Lurs and the Kossaei (Kurds). While counting as part of Eratosthenes' "greater Fars", it would later be included with Jibal. Geography, population, and dialect closely bound the region to Mah rather than Fars. The Bundahishn, in harmony with the wider sense of "Fahlaw" in Islamic times, even places the mountain of Behistun "in Spahan and Kirmanshahan". The actual boundary with Mah must have crossed the Ahmodan (Hamadan)- stakhr road south of Karaj (Rapsa in Tab. Peut. and Ptolemy). Although Spahan is not mentioned in this itinerary, it was an administrative center from Parthian times. Its economic role perhaps grew with both the transfer of 14,000 of its inhabitants to Nisibis and the influx of transported Armenian Christians and Jews. The surrounding districts were notable for their grain production. Strabo (xvi.1.18.34) noted the population as more sedentary than in the Kurdish mountains, but banditry was still prevalent.

Spahan must have connected to the north and east, with the Qum-Yazd road mentioned in the Tabula Peutingeriana. This route linked the districts of cultivation and pasturage on the margin of the desert; it passed from Kashan (Orubicaria) to Ardistan (Pustis), Na'in (Ange), 'Aqda (Rages, Ray), near Ardakan (artacana), Maibud (Tazora), and finally to Yazd (Cetrora). The border with Mah was possibly at Kashan or Ardistan.

-The Cambridge History of Iran, vol. 3(2): The Seleucid, Parthian, and Sasanian Periods, ed. Ehsan Yarshater (NY: Cambridge UP, 1983), 752-753.