Dojima rice traders moved prices at 720 mph with flag relays

The Dojima Rice Exchange in Osaka, formally chartered by the shogunate in 1730 after operating informally since 1697, ran a genuine futures market — merchants across the country needed to know the current Dojima rice price to trade rationally, but Edo-period Japan had no telegraph, no telephone, nothing faster than a human courier carrying a written message. A price that took three to five days to reach a distant city was nearly useless for a market meant to move as fast as trading itself.

A courier network, however well organized, could never beat the physical limit of how fast a person or horse could travel, and anything resembling an electrical signaling system was more than a century away technologically. What the exchange needed was a way to move a very narrow, specific piece of information — a numeric price — over long distances at a speed no courier could match, using only what was physically available: line of sight across mountains and open terrain.

Reduced the price to two digits and relayed it as flag swings across line-of-sight stations, making each hop seconds instead of hours.

Reducing message to digits made each relay a quick glance-and-repeat, not a physical carry.

Sightline spacing turned transmission time into number of hops, not distance.

Narrow vocabulary let unskilled operators staff the network cheaply.

When only a tiny piece of info must move fast, build a purpose-specific visual relay instead of waiting for general telecom.

Reenactments of the system clocked transmission at roughly 12 kilometers a minute — around 720 miles per hour — carrying prices to Kyoto in about 4 minutes and all the way to Edo, across more difficult terrain, in about 8 hours, versus the three to five days a courier needed to cover the same distance.