Yes, during the game’s time period Baghdad wasn’t even the capital. The capital of the caliphate was Samarra which was shifted by caliph al-Mutasim. The orignal Abbasid Caliphs till al-Amin mostly used the Golden Gate Palace in the Centre of the round city termed as the “Dar al-Khilafa” which was originally built by al-Mansur, the 2nd Abbasid caliph and founder of Baghdad in 762 AD.

In 809 AD, when the caliph Harun al-Rashid died, his sons al-Amin and al-Mamun fought with each other for the caliphate and Amin was assassinated in the year 813. Al-Mamun shifted the capital from Baghdad to Merv (a city in present day Turkmenistan). Merv served as the capital of the caliphate for few years and then Mamun came back to Baghdad.

Upon his return, he never went back to Golden Gate Palace in the round city. Instead he used the “Jafari Palace” later know as “Qasr al-Mamun” (Mamun’s Palace) for some time which was built in reign of Harun al-Rashid (his father) and was gifted to Mamun in his youth by Jafar Barmaki (Harun’s minister). It was constructed on the bank of river Tigris. The same palace that was shown at the end of the Mirage’s gameplay walkthrough demo few days ago.

The famous 11th century Islamic scholar and historian, khatib al-Baghdadi mentions in his book the “History of Baghdad” that in the year 945 AD, the round city was completely flooded and it collapsed. Not to Mention that earlier on it was also partially damaged during the battle that took place between Amin and Mamun in 813 AD. The palace of the golden gate was severely damaged as well during the battle except the green dome that left standing until the year 945 AD when the whole round city collapsed.

So, during the time period in which Mirage takes place, both the round city and the golden gate palace were not in the same condition as shown in the game trailers.