Seleucia actually expanded after the Seleucids fell — or, to be more precise, Greek Seleucia survived and gradually merged with the new Parthian royal palace-city of Ctesiphon, on the other bank of the Tigris. In Aramaic the conurbation was eventually known as Mahuza, and later al-Mada'in in Arabic: both mean “the cities”. The combined metropolis had a long and prosperous history from the fall of the Seleucids in 167 BC down to the Arab conquest of Mesopotamia in 637.
Parthian-era Seleucia retained its Greek institutions and part-Greek population long after the Seleucids had disappeared. The Parthian kings relied on the Seleucid cities in their new domains for administration and trade, so they were generally friendly to their Greek urban centers. This policy lasted for several hundred years; the Roman historian Tacitus described it in the year 36 as
the powerful community of Seleucia, a walled town which, faithful to the memory of its founder Seleucus [and] has not degenerated into barbarism. Three hundred members, chosen for wealth or wisdom, form a senate: the people has its own prerogatives.
He goes on to describe how the Parthian kings backed one faction or another in different political struggles inside the city — indicating that the city retained both political autonomy and the classical Greek fondness for factionalism. Pliny the Elder, writing around the 70’s, described the city as “retaining its freedom and its Macedonian manners” and said it had a population of around 600,000 — a number which may not be accurate but which makes it around the same size as contemporary Alexandria, and thus probably the second or third largest city in the world.
A wordy coin of Gotarzes II (40-51 CE), minted in Seleucia. The reverse shows the king receiving a wreath from Nike (“Victory”), a traditional Seleucid coin design. The legend reads BAΣIΛEΩΣ BAΣIΛEΩN (“king of kings”) above and not very legibly down the left EΠIΦANOVΣ ΦIΛEΛΛHNOΣ (“the revealed” and “the friend of the Greeks”).
Tacitus’ note marked something of a turning point: In 36 the Seleucians supported the wrong claimant to the Parthian throne; seven years later the eventual victor in the Parthian civil war, Vardanes I centralized more of the Parthian royal government across the river in Ctesiphon, and a few years later Ctesiphon became the primary Parthian capital. A permanent royal residence accelerated the merging of the two urban areas and the prosperity of the region. Royal patronage and an excellent position on the booming silk route, plus a strong agricultural base and the traditional river trade of Mesopotamia made the combined city wealthy and powerful.
However, during the long series of Roman–Parthian Wars Seleucia-Ctesiphon was the natural focus for Roman operation in Mesopotamia. Roman armies captured the city in 116 (during Trajan’s brief conquest of Mesopotamia), 164 and 197. Its reported that the sack in 197 produced 100,000 prisoners — almost certainly an exaggeration, but a telling one.
The capture of Seleucia-Ctesiphon in 197, from the arch of Severus. Photo: Jona Lendering
When the Sassanids overthrew the Parthians — helped, no doubt, by the crushing defeat in 197 — they too used it as one of their capitals. Renamed Beh-Ardašīr for the Sassanian emperor Ardashir I, it continued to flourish until about the middle of the sixth century when devastating floods rendered the city partially uninhabitable. By the time of the Arab conquest in 637 the population was under 150,000, a quarter of its Parthian peak. Basra and then Baghdad eclipsed the city as the primary urban centers in the region.
Like Babylon before it the city was not “destroyed” — it simply withered away as economic and political life moved elsewhere.
The ruins of the Sassanid palace in Beh-Ardašīr as they appeared during World War I