Alternate history transport

[PTTG]

At some point in the history of Rome, the cultists of Poseidon are granted a boon; so long as they worship him, they may build canals that flow uphill and down with ease. They also may move ships at sea with equal speed.

This allows the Roman Empire to remain united, to transport goods far faster, and all around be more stable. No other magic nor divinities challenge Poseidon, and within a century he's become the chief god of the pantheon. Iesu, his demigodly son and patron of forgiveness, is a moderately important figure in time.

The Roman empire, meanwhile, expands throughout Europe, building canals that crisscross the continent. Elsewhere, religions are in turmoil, frantically seeking a way to prove the Romans to be somehow duplicitous, or perhaps in league with demons...