What time is it? Ask around ancient Rome and you may get a dozen different answers. While our lives are rigidly scheduled down to the minute, time was a more fluid concept in past times. The passing of the day was marked instead by the progression of normal events. When in doubt, one could always reference the position of the sun in the sky. Across the ages, high noon was a convenient time to schedule a Western showdown, or in the case of ancient Rome to make sure the sundial was positioned correctly.
In Rome, the largest sundial (roughly 200 by 525 feet) stood in the Campus Martius. It's time-telling shadow was cast by an obelisk brought from the Egyptian city of Heliopolis (it still stands today in the Piazza Montecitorio in modern Rome (see picture). Lines of bronze set into the pavement allowed passers-by to tell the hour and date by the position of the shadow cast. Romans considered it a social event to stop by the large sundials at the Campus Martius or the Forum to check the time, though there were smaller sundials throughout the city on buildings and in courtyards of wealthy homes.
Though the wrist watch Charlton Heston allegedly sported in Ben Hur was an anachronism, the Roman's did have their own version of a wrist watch. They looked liked concave shells just over an inch in diameter. Sunlight passed through a tiny hole on one side of the shell and cast a bright dot onto the set of markings carved into the concave surface. Though the well-to-do Roman could count on his solaria to tell the time from the convenience of anywhere he pleased in Rome, he wouldn't be able to take it with him on his travels. The markings were calculated precisely to the sun's positions over the latitude of Rome alone. They also needed a seasonal adjustment.
Water clocks were also a common way to gauge the time, and could even be used at night or on cloudy days. Like an hourglass dropping sand, these devices dripped water at a given rate into a vase that was marked to indicate hours at rising depths. Some were constructed with special floats that triggered sound-making devices, a sort of predecessor to the cuckoo or grandfather clock. The clock could even be used as a timer. Wax plugs could be used to stop the flow in case a timed senate speech or race event was interrupted. However, like the sundials, only the wealthy could afford them. Timepieces in ancient Rome were status symbols rather than necessary evils.
In any case, you might say you would be just as likely to hear the question 'Do you have the time?' on the streets of Rome as you are to hear this reply: 'Movate, tu es in meus lumen!' which roughly translates to "Move, you're in my light!"