βῆ δ᾽ ἴμεν
This familiar Homeric expression is a good, straightforward example of a formula with a fixed metrical position. There is flexible variation within the formula: it can be expressed in the third-person singular, as here, as well as in the third-person plural (as at 10.297: βάν ῥ’ ἴμεν), and it can use either the conjuction δ’(ε) or the particle ῥ’(α). But in the more than thirty uses of all these permutations in the Iliad and Odyssey, the formula always begins the line, occupying the first foot. Thus this specific way of saying “he/she/they went/left” can be assumed to have been particularly useful at the beginning of the line for the singer as he composed in performance. The formula gains additional flexibility with the use of the later Aeolic infinitive form ἴμεναι (the Aeolic infinitive form ἴμεν is earlier), which extends the phrase into the second foot. We see that version of the formula at least fifteen times. Another version of the formula with the Ionic infinitive form ἰέναι (so either βῆ δ’/ῥ’ ἰέναι or βάν δ’/ῥ’ ἰέναι) likewise extends into the first syllable of the second foot, and this iteration shows up at least eighteen times in our texts: see examples at 10.136, 10.179, 10.273, and 10.336. The only case in which we see this phrase in a metrical position other than the initial position of the line is when it is part of a longer formula, an example of which we see at 10.73. In this longer formula (which also appears in Iliad 20.484 and Iliad 21.205), the line begins αὐτὰρ ὁ βῆ ῥ’ ἰέναι μετὰ and is completed by a name + epithet formula. This longer formula is used in cases of going after/for a specifically named person, while the various shorter versions can be used in a wide variety of situations of going, but always when the singer starts a new line. Because this formula is used seven times in Iliad 10, we can also see that many men are in motion during this night.