When one presents a petition to a royal, how does one act? I've only had time for a very brief survey, but here are my results.
First are a few notes from reading the book "Begging Pardon and Favor: Ritual and Political Order in Early Medieval France"Geoffrey Koziol 1992, which is handily available as a google book as well as from a number of Australian libraries.
Kozoil (p8) says that "Supplication is simply the act of begging a favour or forgiveness in a formal language of entreaty" As such supplication has many forms, depending upon the circumstances, but it is a verbal request for action in formal language accompanied by some gesture of humility. It presumes there is a petitioner and a person with the power to grant the request.
The gesture in early medieval France could range from something as simple as bowing the head or outstretching the hands to kneeling or prostrating oneself before. "All that was essential was a formal language of entreaty that communicated two facts: the petitioner's humility and the benefactor's graciousness." (Kozoil p8)
A most common posture of supplication whether standing or kneeling was raising both hands upwards to the person of authority. Or the petitioner might have head and shoulders bowed to the ground. 12th C letters where a petitioner writes instead of being physically present mention kneeling or prostrating themselves in supplication (if only they were there), in a variety of ways indicating this was the common practice of the time, and wasn’t just a formulaic way of writing a petition.
Following this reading, I tried to find some images of supplication. Kozoil says there is not a lot of difference between supplicating oneself to a religious (be it earthly or heavenly i.e. prayer) or secular authority, so I've pulled together both examples here. Well, what I think are examples of supplication - I could be wrong on some of them.
Concluding from the pictures, the body posture of supplication seems to be quite flexible as noted in the above book- one can be standing, bowing slightly, in any of a variety of kneeling or partially kneeling poses or even prostrating oneself on the floor. One presumes the lower to the ground, the more abject ones' supplication. Eyes are either downcast or looking at the object of veneration. The hand position of supplication seems to be: Hands apart, palms toward the figure of authority, fingers above hand either slightly spread or together, thumb separate. If you are holding an object, you may use only one hand in this position.
All in all, the idea of supplication seems to have worked it's way quite effectively into the modern psyche essentially unchanged. The rather fantastic depictions of medieval life in Hollywood movies depict supplication in these terms (although they may exaggerate the degree of humility needed for the circumstance), and the general concept is alive and well in modern actions such as begging a person for a favour with humility, kneeling to pray or getting down on bended knee to propose marriage. The only change I can see is that the hand posture modernly is more likely to represent the modern christian gesture of prayer - hands together - than the hands apart gestures or prayer or supplication depicted above.