Why did Surat Ar-Rum begin with (Alif, Lam, Meem)?

Surah Ar-Rum opens with the disconnected letters "Alif, Lam, Mim," like other surahs, and this is one of the aspects of the Qur'an's miraculousness. Despite these letters being accessible to Arabs, they cannot formulate anything like this Qur'an. The word of Allah Almighty is completely different from the speech of humans, which distinguishes it and makes it miraculous. This is supported by the words of Allah the Almighty: (Say, "If mankind and jinn were to gather in order to produce the like of this Qur'an, they could not produce the like of it, even if they were to each other assistants.") After its opening, the surah presented a truthful prophecy about the Byzantines' (Romans') victory over Persia within a few years, which was considered impossible in the eyes of Arabs at that time, and this divine promise was fulfilled.