As someone whose boyish fantasies ran along the lines of "What would have happened if the Romans had invented wireless?" (they could have, you know. They had all the bits), I have nothing but love for the Antikythera Mechanism - the 2000 year old precision clockwork astronomical device discovered in a Grecian shipwreck.
Long recognised as an instrument for calculating time, the latest discoveries - reported in Nature as part of a burst of new information following high-precision computerised scans - show that it not only predicted planetary positions and generated dates, it also linked local events such as the Olympics and monthly calendars to much longer cycles of decades that reconciled lunar and solar timekeeping.
in short, it was a very sophisticated mathematical device that was intrinsic to long-term planning, implying that the Greeks had a much more complex concept of practical calendrical matters than we thought.
Which is enthralling in its own right -- and only makes my inner childhood nerd leap up and down excitedly, asking "So if they could do that, why didn't they..." with ever more urgency. And by induction, what is it that we're not doing with all our cleverness that the small geeks of 4000AD will find so difficult to understand?