Mathematician Alain Connes cites a French legal rule that explicitly accounts for propagation of information at finite speeds substantially below the speed of light:

There was a legal rule according to which a law decreed in Paris on day J was applicable in Paris on day J, but it was valid at distance n km of the capital only on day J + 1, at distance 2 n km on day J + 2, and so forth, where n is the number of kilometers covered by a stagecoach in one day.

Large ancient empires, such as the Roman Empire, must have seen similar situations very often. (E.g. the emperor makes decision X in Rome on day J, but it's yet unbeknown to the governor of a remote province when he partially counters it with decision Y on day J + 1).

How did the Romans and others deal with these situations? Was it completely ad-hoc or did they also have special applicable rules in their legal codes? (Although I'm referring to an emperor in my specific example and emperors may not have been constrained by legal codes, relevant situations must have also occurred e.g. in private business across the Mediterranean.)

UPDATE This week´s Economist carries an article about the economics of interstellar flight which makes for interesting related reading. It cites an early (perhaps tongue-in-cheek) paper by Paul Krugman who even came up with two fundamental theorems of interstellar trade :-)

Such trade will be affected by relativity theory, which shows that beings on Earth (or Trantor) will see time pass at a different speed from those who are on board cargo ships moving between the two. This could make it hard to calculate the net present value of a shipment. And the fact that messages can move at best at the speed of light (and cargoes more slowly still) might do odd things to the ability to arbitrage between the economies of the two worlds.

As I thought more about the question I was also reminded of George Nashes biography of Herbert Hoover: Hoover was sent to Australia in 1897 as a young mining engineer. A visit to headquarters for a thorough briefing was a then especially important part of his preparation because instant world-wide communication was impossible and relatively junior persons had to make independent decisions on the spot. Presumably this was even more the case e.g. for say imperial generals in ancient times and is less the case today.

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    As a general comment: Laws didn't change often enough for this to be a significant problem during ancient times. But when laws changed, they would probably be rendered applicable when the local court knew about them. I don't know much about the Roman legal system though. – Lennart Regebro Oct 11 '13 at 11:50
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    I agree with @LennartRegebro, the laws would be enforceable once the local court knew about them. To avoid specific propagation delays, empires could use the same approach as we use today (though for other types of delay) - have the new law come into effect well after the initial proclamation. i.e. Proclaim on one new year's eve and enforce everywhere on the next new year's eve. – LateralFractal Oct 11 '13 at 11:57
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    @LennartRegebro You're right about this simple rule, yet at least the French apparently decided for another explicit rule and presumably did so for some good reason (and not just legal over-engineering, one would hope). I'll fill in a better example if one comes to mind. – Drux Oct 11 '13 at 12:35
  • @LennartRegebro A somewhat better example could perhaps involve a local court that obeys the governor and may not admit knowledge of the "far-away" emperor's decision at any time that is inconvenient to the governor. The emperor could still learn about such goings-on by employing a trusted messenger to the local court, but it now gets pretty messy and ad-hoc. E.g. a reference to simple physical laws (as in the cited French law) would now seem to help (if not from the governor's perspective, though :) – Drux Oct 12 '13 at 7:21
  • Sure, but that's still just really relevant if laws change often. Ancient laws are often coded either in religion, or engraved into stone slabs and risen around the country. Which day a law was enacted is irrelevant, the question is under which king. :-) – Lennart Regebro Oct 12 '13 at 7:27

See article II of the Treaty of Ghent, ending the War of 1812. http://war1812.tripod.com/treaty.html

It lays out a series of delay times for many different parts of the world for the terms of the Treaty to come into effect.


I'd say that accounting for propagation delay explicitly with the day + n method is the exception rather than the rule. The most common accounting for this is to consider the law/edict in effect only when it is officially received.

Thus the process goes like this:

  • After drafting the edict, the sovereign signs or seals an edict, indicating authenticity and preventing tampering
  • The edict is sent via messengers to the recipient
  • Receiving the edict is sometimes a ritual, and the messenger bears witness to the event. From this moment on the edict is in effect

Obviously the messenger service is a highly privileged one, with severe consequences for any obstruction.

For example, the process of announcing an edict applicable to the entire Qing Empire was very elaborate:

  • The edict was drafted by the innermost cabinet,
  • edited by the Grand Secretariat,
  • written and signed/sealed by the Emperor according to a specific format,
  • taken to the top of Tiananmen and read aloud as a ceremony,
  • taken to the Ministry of Rites and multiple copies made,
  • each copy sent to regional governors, who would in turn repeat the reading, copying and sending steps until the edict reached all levels of government
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    Did they also include a "start date" on the edict so that some provinces didn't end up applying the law before others? – LateralFractal Oct 28 '13 at 2:39
  • Thx, but this is essentially what @LennartRegebro also explained in his earlier comments, isn't it? The question is specifically about the more exceptional case (in your terminology). – Drux Oct 28 '13 at 12:17

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