I daresay that if skies were clear over London and Rome right now; a sundial would NOT read the same time at both places.
Water clock (330-350 BC)
It might divide up LOCAL time correctly; but how do you synchronize the London and Rome clocks?
You think? Anyway, the ancient’s calculations were off by few hundred to a thousand miles. But, still not bad for the ancients using dials, and poles. Gotta give it to them for their ingenuity and desire to know the universe. Mans’s curiosity is boundless. By the way, I made my 4th grader use the same method to figure out the circumference of the Earth, and he was off by 110 miles. The flaw being that the earth is not round.