τρισκαιδέκατον
The number thirteen seems to be almost a “round number” or to have a completing or capping aspect to it in Homeric diction. Just as the most important victim, Rhesos, is thirteenth, Alkinoos counts himself as the thirteenth basileus among the Phaeacians (Odyssey 8.390–391). Similarly, when Odysseus chooses men for the mission to investigate further the land of the Cyclopes, he chooses twelve, counting himself as thirteenth, although the number itself is not cited there (Odyssey 9.195–196). Thirteen also seems to round off or cap lengths of time, such as the thirteen months that Ares is held bound in chains by Otos and Ephialtes before Hermes rescues and frees him (Iliad 5.387). It is on the thirteenth day that Odysseus and his crew leave Crete after being trapped there by a north wind (Odyssey 19.202). When Odysseus recounts to Laertes the gardens his father had promised him as a young man (as part of proving his identity to him), the numbers are all what we would consider round (ten apple trees, forty fig trees, fifty vines), but also include thirteen pear trees (Odyssey 24.340). Perhaps the completing aspect is related to the lunar calendar, the year coming round in the thirteenth moon. Germain (1954:10) includes thirteen among numbers that are “presque fantomatiques.”