From ‘The Grand Chessboard’ (1997) by Zbigniew Brzezinski

Even so, the Roman Empire was not unique. The Roman and the Chinese empires emerged almost contemporaneously, though neither was aware of the other.

It is not entirely true. There are mentioning of a big empire in the far west named ‘Great Qin’ (大秦) in ancient official documentation e.g. the Book of Late Han. But the majority of populace probably did not know it.