You Need Redundancy And Back-Up Systems

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From the years 540 to 562, the Eastern Roman Empire under Justinian was engaged in a drawn out struggle against the Sassanid Persians under Chosroes (Khosrow).  This contest is usually called the “Persian War.”  Many illuminating incidents that happened during this conflict I have used in previous articles here.  Another one highlights the need for redundancy and “back-up” systems as security in times of trouble.  We are aware of this principle when it comes to computing and software, but it can be applied to many other fields of activity.  The following story demonstrates this principle.

When Chosroes had captured the Syrian town of Petra, he immediately fortified it, believing that the Romans would make strenuous efforts to retake the town.  Water resources were then–as now–a vital part of a city’s defenses.  He knew that one of the first things the Romans would do during a siege would be to cut the aqueduct bringing water into the city.  So he devised the following plan.

He ordered a very deep trench dug, and into this trench he layered three water pipes successively.  He first laid down one pipe, and then covered it with mud and gravel.  Then he laid down another series of pipe-works, and covered those with dirt and sand.  And then–above ground and visible to the unaided eye–he laid the third series of pipes.  So now he did not just have one pipeline, but rather three independent networks of pipeline.

When the Romans began the siege of Petra, they did not fully understand this.  They cut the first pipeline, and assumed that doing so would bring the defenders to their knees.  They were not thorough, and failed to make deeper investigation into the matter.  As time went on, it became clear that the city was still somehow getting water.  But the Romans could not understand how.  By interrogating some captured residents of Petra, they finally realized that there was another water pipeline.  So they dug down and found the second pipeline, and cut it; this, they thought, would be the end of the matter.

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Yet the city still maintained its supply of water; and the Romans could never understand how.  Chosroes had not even told the residents about the third pipeline:  this was to be his state secret.  Even if someone were captured, he would not be able to divulge something he was unaware of.  When the Romans finally took the city by storm, they eventually discovered how they had been deceived by the three pipelines.  They admired the care and diligence that Chosroes had taken to prepare such an elaborate back-up system.

And now they showed the defenders that they were still Romans, and could compensate in ruthlessness what they may have lacked in subtlety.  The Roman commander, Bessas by name, sent all the prisoners of Petra off to his emperor; he then razed the walls of Petra to the ground so that the city could never pose a problem for them again.  From this story we can see the importance of thorough planning and preparation for any enterprise:  and when it comes to security for things that matter, we must not rely on just one system.  We must have several back-up systems in place.  Redundancy is defense-in-depth; and this is security.

This is the story of Chosroes’s pipelines as described by Procopius in his Wars (VIII.12).

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