Why the people pray kneel and with the joined hands?

At the time of the conquests Romans, the defeated ones in the fights ran in direction to the victorious people, were kneel and extended the hands asking for to be chained. This attitude of suplication was spread out in the Christian Age. Christ was had as the conquering the holy ghost of all the peoples and the fidiciary offices repeated the attitude of humildade of the loosers in the hour to pray.