From A Wiki of Ice and Fire
The Clanker Lords is the mocking style that the sellsword companies gave Chezdhar zo Rhaezn and his brothers Maezon zo Rhaezn and Grazdhan zo Rhaezn who came up with the idea of chaining all their slave soldiers together so they cannot flee when facing Daenerys Targaryen's Unsullied (as their previous soldiers did). They are chained together in groups of ten, wrist to wrist, ankle to ankle.
The slave soldiers march at a snails pace due to the weight of their chains. Beans observes that you can hear them clanking ten leagues off.
None of the poor bastards can run unless they all run, and if they do all run, they won't run very fast.
- ↑ 1.0 1.1 1.2 A Dance with Dragons, Chapter 25, The Windblown.