Taq Kisra (seat of emperor) at Ctesiphon or Tesfon
Tesfon was an ancient city in Mesopotamia (now Iraq), founded by the Hellenic Greeks and was later developed by Parthians and Sasanian Iranians. It is located on the eastern bank of the Tigris river and is about 35 kilometres (22 mi) southeast of modern-day Baghdad. The city emerged as a combination of smaller towns in proximity to each other, especially Seleucia, which was the capital of the Hellenic (Greek) Seleucid empire - a successor state to Alexander's empire, founded by one of his generals after his death in Babylon.
Babylon as a biblical city was abandoned during the Greek Macedonian dominion over Mesopotamia. Its inhabitants were relocated to the newly constructed city of Seleucia, as its successor. After the fall of the Seleucid empire at the hands of the Parthians (an east Iranian people), Seleucia was enlarged into Ctesiphon by the Parthian emperor and remained as an emperial center and later capital of the Parthian empire. The Sasanids (a clan, a combination between Persians and Kurds of Kermanshah) later dethrowned the Parthians and Ctesiphon served as their novel capital. The city rivaled Rome and Constantinople during its days, for over eight hundred years, until the emergence of the 1st Islamic empire, known as the Rashidun Caliphate, which burned the city to the ground.
In 600 AD, the still emerging 1st Islamic empire began a series of military campaigns into the Byzantine (East Roman) and Sasanian territories in Middle East and North Africa, which were bitter enemies for centuries and had weakened each other as a result of continuous wars. As a result, Ctesphone was captured by the victorious Arab armies and was subsequently incinerated by the direct orders from the Islamic caliphe (king) Omar Ibn Khatab, as a show of force and divine victory - something that the Might of Rome and Byzantine had not been able to accomplish, a primitive, still emerging Islamic empire was able to do with ease. The devout Arabs took that as a sign from God, to grant them victory and proceeded the military campaigns. The fall of Ctesphone marked the beginning of the "Arabization of Mesopotamia", which saw a mass migration of Arabs from the Arabian Peninsula, their original homeland, into Mesopotamia and resulted in a permanent demographic shift of the area. The inhabitants of the city, comprising of mainly Persians, southern Kurds (Fayli) and native Babylonians (known as Chaldeans) were massacred or taken into slavery by the Muslim armies - very akin to the Fall of Constantinople.
Even after the demise of Ctesiphon, the area still was viewed as being of great importance. Therefore, the colonizing Arabs founded a new city, as a substitute for Ctesphone, in proximity to it, which is the present-day Baghdad. It too served as the capital of now Abbasid Islamic Caliphate for quiete sometime but was later destroyed by the invading Mongols in later Middle Ages. Nonetheless, it was rebuilt and still serves as the capital of the new (Arabic) state of Iraq (Mesopotamia).
That is how Ctesiphon fell, Iraq became Arabic, Baghdad was born and finally Babylonians (nowadays Christian Chaldeans) lost their homeland and almost have gone extinct.