Also from mediaeval times: "To get on one's high horse", which nowadays means to react indignantly, or to take an agressive stance in argument.

In battle, something the size of a carthorse was required to carry a knight encased in armour (and sometimes armour for the horse also) at anything like a gallop. This was the destrier, or "high horse".

To save its strength, the destrier wasn't usually mounted until the moment of battle arrived. It was usually led by the squire or varlet, while the knight pottered along on something hardier and more willing, the ambling palfrey.

When the knight "got on his high horse", combat was imminent.