The game of Trigon was played by three players standing at the corners of a triangle, and was played with a hard ball, also known as a trigon. The impression from the references is that the trigon does not bounce, perhaps being very much like a baseball or softball. The harpasta (bouncing handball) is never confused with the trigon.
The rules of Trigon have never been successfully reconstructed. The object of trigon was apparently to throw to another player such that he either could not, or perhaps could, catch it. Feinting plays a part in this game and two balls could be in play simultaneously.
Catching a ball left-handed was the sign of a skilled player. Transferring the ball from one hand to the other seems to have been part of the action, in which case feinting may be embodied in this technique along with a reversal of clockwise/counterclockwise play. Batting a ball back rather than catching it seems to have been considered skillful play. Missing a catch was apparently a score for the opponent, per Martial's epigrams. To be "struck" with a ball (and not catch it?) seemed to be part of the object. Since scorekeepers were used, the possibility exists that very complex scoring was involved (that is, left-handed catches could be 2 points, batting a ball maybe 3 points).
Trigon is probably the "glass ball game," a reference to a famous player, Ursus, who was so good he played with a glass ball, and never once dropped it. In fact two such glass balls have been found so far. One of them is shown in the images above and below, where the exact size can be seen in the palm of a hand. This glass ball has a decorated surface, and due to the fact that it is broken, is known to have been made from a composite of recycled colored glass.
A translation of Plautus is provided by Alexander Adam:
Here a descriptive passage from Seneca, who happened to live next door to the baths:
The game Seneca refers to here is surely Trigon. The court is the palaestra next to the baths, where both weightlifters and ballplayers would engage themselves. Seneca implies the ballplayer counts his throws from the start. This suggests that the number of throws made (and caught?) are counted. This might also explain why a pilecripus is necessary, although this passage seems to indicate that the ballplayer, the trigonali, does his own counting. Perhaps most ballplayers did not have the luxury of an individual pilecripus.
Although the Romans probably inherited Trigon from the Greeks, there is no record of this game being played in Ancient Greece. However, it was played in Ancient Egypt as far back as 2500 BCE. That's when these two tomb paintings have been dated, from the tomb of Kheti in Bani Hasan. The tomb is filled with images of athletes, epsecially wrestlers, and Kheti is referred to as "beloved of Sekhet, Mistress of Sport." The image on the left shows three girls playing with two balls in play, while the image on the right shows three balls in play. No other ball game known is played in this fashion. Observing the two Egyptian images and the redrawn image above from the Baths of Trajan in Rome, it is hard to escape the impression that the game resembled or involved juggling.
The Ball Game of the Satyricon -- Is this Trigon?
Balsdon (Ref. 6) considers this to be the game played by Trimalchio in the Satyricon, but this highlights the incongruencies. Trimalchio is described as bouncing the ball, but the trigon isn't a bouncing ball. The Satyricon twice mentions the circle around which the players stood, but trigon is played around a triangle. Balsdon states that trigon was a serious game with each player having his own scorer, and his own ball-boy. In the Satyricon there was only one scorer. Trigon is played by three players, presumably, but Trimalchio plays with a "bunch" or a "troupe" of boys.
Furthermore, Trimalchio does not seem to be any kind of serious ballplayer; he was wearing sandals and playing the game purely for leisure. Playing more than one ball at a time is difficult to conceive in Roman Ball, as we have defined it, but in a three-man game like trigon, play might be sequential (clockwise) like a three-court version of volleyball without a net. The scoring of Trimalchio's game could be done by counting either the catches or the misses. In Trigon, the ball is scored only when it is dropped, although atches may have been scored up to 21 points, at which point the game would likely end as a tie if no ball had been dropped.
On the other hand, with more than three players they might be forced form a circle. In fact, the arguments presented above are not conclusive. There may even be problems with the translations; as the exact meanings of the more esoteric and specific Latin words remain obscure to us.
Some Proposed Rules for Trigon
These are untested and provided here for experimental purposes. If anyone tries these, we'd be most interested in your impressions or suggestions.
The Rules of Trigon
Here Martial makes reference in an epigram to Trigon, Harpasta, and a game of catch(?) played with the follis or large bladder-ball:
Martial makes further reference to Trigon and the advantage of left-handed throws:
M. Cornelius Fronto says in one of his letters:
"He that sends too heavy a gift offends no less than he who sends his fellow ball-player too heavy a return or toasts his fellow guests with a big cup."