Imagine what would happen if some one threw a bunch of them before a calvary charge? When horses stepped on them, they would lose their footing and tumble, causing the ones behind to bunch up.
A military devise to defeat or break up calvary charges.
The Romans beat the Sarmatians (among others) and brought them into their own auxiliary ranks, so they had that covered. Could be though, because they’d beaten the barbarian horsemen in the first place.
In the middle ages, in Sicily, the saracens scattered broken pottery to prevent a cavalry charge. Hardraada was still in service to the Byzantines, and he and his men just cut palm fronds off nearby trees and wrapped their horses’ hooves and lower legs, and charged. :^)