Upon the beginnings of chaos in the lands of the Rising Sun, lords were beginning to become ambitious and rebellious, leading to rouge castle incidents that required the rapid advancement of siege weaponry. One of the earliest, and most effective models, was a model devised by legendary samurai Shirotori Mutsu after being ordered by his lord to come up with a way to siege the enemy castle, with a deadline of two weeks.
Shirotori Mutsu saw his lord's retainer with a Jumonji Yari next to his lord's Palanquin and the rest is history.
Even in the advent of Karakuri Warfare, these models are still seen often on the field.