Horses can be ridden but always were driven too. This needs a harness. The first harness of course was for ploughing. But very early a cart was used, first driven by one horse (Homer tells about), then two (the Hittites used it against the great Pharaoh Ramesses II.), then three the Russian troika (three horses drove a sledge in great speed (Tolstoy), then four and more (coaches of “modern” times, I know them from the novels of Georgette Heyer) or the cart driving Elijah up to heaven. The number of four horses is also known to us from the apocalypse of St. John ( a white horse….a red horse….a dark horse….a pale horse). In fairy tales the “prince” often needs those horses to get the princess. The number four:
“Four days were spent in thinking what name to give him, because (as he said to himself) it was not right that a horse belonging to a knight so famous, and one with such merits of his own, should be without some distinctive name, and he strove to adapt it so as to indicate what he had been before belonging to a knight-errant, and what he then was.” (Don Quixote thinking what name to give to his horse). Don Quixote of course was not driving, but a riding knight-errant…..
But when we think of Troika we should rather think about the number three, shouldn’t we?