This is the hadith.
Abdullah said that five signs have (become things) of the past (and have proved the truth of the Holy Prophet):
(Enveloping) by the smoke, inevitable (punishment to the Meccans at Badr), (the victory of) Rome, (violent) seizing (of the Meccans at Badr) and (the splitting up of) the Moon.
Now, Abdullah (the narrator) is saying that these have become things of the past, which implies that Rome has already been conquered, but Rome was never conquered by the Muslims. Attempts were made, but the Muslims never succeeded. So, according to the hadith, will the conquest of Rome by Muslims take place in the future?