Quote from SNBthetrue:
I think that it was the day that one Emperor and his advisers realized that it was under the Law of the Empire that the Christ had died...
theirs hearts were so broken that they didn't took care of it anymore...
It was the day that the all known world lost its value to them...
You demonstrate a lack of historical knowledge here... and when that happens, it's not unusual for one to cling to religion as a factor.
Rome became an empire after the civil war between Marc Antony and Augustus (then known as Octavian) ended with the battle of Actium in 31 BC.
Jesus supposedly died around 30 AD, give or take a few years. That's 60 years after Augustus' ascension, and the death of the Republic and the beginning of the Empire.
Rome was sacked in 410 AD by Alaric the Visigoth almost 400 years after Jesus' death, then again in 455 AD by Geiseric the Vandal, and was depopulated by Totila, King of the Ostrogoths in 546 AD. Rome did not really fall in one day, it was a process of devolution.
During that decline, Constantine moved the capital to Byzantium, named that city Constantinople around 306 AD. Rome was considered the "western" capital, while Constantinople was the Eastern capital. The Byzantine Empire followed for about another 1,000 years. It was Christian in nature, only because Constantine saw that it was politically expedient. Many Orthodox Christians even viewed Moscow as the third Roman Capital.
Then in the Middle Ages, Rome rose again with the new power structure based in the Vatican. Rome's influence was seen in the rising city states of Florence, Venice, and before that Charlemagne...
It's a long history, but if you view ancient Rome, Imperial Rome, Byzantium, and the Vatican as various "forms" of Roman power... Than it's not out of the question to say that Roman influence and power lasted between Julius Caeser in the 40sBC to the 1800s AD. A nearly two thousand year reign in one form or another.
To say that one single Emperor's thoughts of Jesus was a turning point is kind of simplistic and ignores a lot about Rome's real influence and power through many centuries.