my admiration for the excellent conversion and paintjob
apart from the missing "dwarf" who was driving the cart, this contraption perfectly evokes the situation from
"Lancelot, le Chevalier de la Charrette". Due to lack of detail knowledge, I cannot confirm the existence of such carts for medieval times, however, due to Chretien de Troyes using the symbolism of this plot device in 1170,
http://en.wikipedia.org/wiki/Lancelot,_the_Knight_of_the_Cart#Significance_of_the_Cartit can be stated without doubt that malefactors must have been transported in some sort of cart (it would be pointless to mention it otherwise).
It now takes little interpretation to assume that some sort of device to impede said criminals from escaping their means of transportation/humiliation would be necessary, and a cage appears not too far fetched.
I would have no historical reservations of any kind to place my Lancelot figure in it