What was the importance of Crusades during the Roman Empire?

Please note that there were not any Crusades during the
time of the Roman Empire.  The Crusades did not start until the late 11th century and
the Roman Empire is usually said to have fallen in the late 5th century.  In addition,
the Crusades were fought against Muslims and the Muslim faith did not come to be until
the 620s.  Therefore, there could not have been any Crusades in the Roman
Empire.

You have tagged this with "empire split."  I wonder
if you are referring to the fact that the 4th Crusade ended up taking not Egypt, like it
was supposed to, but the city of Constatinople.  Constantinople was the capital of the
Eastern Roman Empire, which became the Byzantine Empire.  By taking Constantinople, the
4th Crusade helped in a small way to further drive the Orthodox Church (in what used to
be the Eastern Roman Empire) from the Roman Catholic Church (in what used to be the
Western Roman Empire).

However, it is important to note
that there were no Crusades during the time of the Roman Empire.