Short answers, pulled from the story.
Seleucia was founded by Seleucus I Nicator, one of the successors of Alexander the Great, around 305 BC. It served as the first capital of the Seleucid Empire and was built in part by forcibly relocating the population of Babylon to the new city.
Ancient texts claim Seleucia reached a population of 600,000. Excavations show the city walls enclosed at least 550 hectares. At its height, only Rome, Alexandria, and possibly Antioch were more populous.
Seleucia was burned by the Roman emperor Trajan in 117 AD but was subsequently rebuilt by the Parthians. It was completely and finally destroyed in 165 AD by the Roman general Avidius Cassius, after which it was never rebuilt.
The Council of Seleucia-Ctesiphon, known as the Synod of Mar Isaac, met in 410 AD under the presidency of Mar Isaac, the bishop of Seleucia-Ctesiphon. It declared the bishop of Seleucia-Ctesiphon the primate of the Church of the East and granted him the title Catholicos, making no bishop election valid without his approval.
The site of Seleucia was rediscovered in the 1920s by archaeologists who had been searching for the city of Opis. University of Michigan professors Leroy Waterman and Clark Hopkins led excavations from 1927 through 1937, followed by an Italian mission from the University of Turin directed by Antonio Invernizzi and Giorgio Gullini between 1964 and 1989.
Excavations at Seleucia recovered bronze coins, salt receipts bearing the city's name, a blue glazed incense burner now in the Baghdad museum, a Greek-inscribed stele, and surgical instruments. The Italian mission found a Seleucid archive building containing approximately 30,000 seal impressions, all in a fully Greek style, along with a reused brick stamped to 821 BC.