Short answers, pulled from the story.
Seleucia emerged from the ashes of Babylon around 305 BC when Seleucus I Nicator ordered a massive population transfer. He forced almost all inhabitants of Babylon to leave their ancient homes and resettle in this new city on the west bank of the Tigris River.
The original site eventually faded into obscurity and was swallowed by desert sands after the Tigris shifted its course. It sat at the confluence of the Tigris River with a major canal from the Euphrates, positioning it to receive traffic from both great waterways.
Mithridates I conquered the city in 141 BC and made it the western capital of the Parthian Empire. A senate of 300 people ruled the city while ancient sources claimed 600,000 inhabitants lived within its bounds.
Roman general Avidius Cassius completely destroyed the city in 165 AD, ending centuries of prosperity. The Roman emperor Trajan burned down Seleucia in 117 AD during his conquest of Mesopotamia before Hadrian ceded the city back to the Parthians the following year.
The Council of Seleucia-Ctesiphon met in 410 AD under the presidency of Mar Isaac, bishop of Seleucia-Ctesiphon. This synod declared the bishop of Seleucia-Ctesiphon as the primate of the Church of the East with the title Catholicos.
American archaeologists rediscovered the site of Seleucia in the 1920s while searching for ancient Opis. University of Michigan professors Leroy Waterman and Clark Hopkins oversaw excavations from 1927 through 1937 on behalf of the American School of Oriental Research.