I've seen a couple (pop-ish) sources say that the Immortals (maybe 10k strong) of the last Persian empire (7th century) would chain themselves together to demonstrate total devotion to battle and their unit. Is this really true? I can't really find official sources that confirm it and it seems like a terrible strategy for maneuvering troops on a battlefield. I know that part of history can be known for some artistic flair.
According to the Circle of Ancient Iranian Studies, 'chained' is a misunderstanding of the word 'silsilah', from the work of a writer named al-Tabari. They state that it is a poetic device used to describe troops organized in units and standing in rank:
https://www.cais-soas.com/CAIS/Military/sasanian_military.htm
Also, if the expression was literal, a large part of the baggage train would have been taken up carrying these chains, and the troops would have to be willing to march to a battlefield and then stand around and allow these chains to be fastened to them. I cannot really imagine any of this occurring in a scenario that would be plausible.