Iambic Senarii, Iambic Septenarii and Iambic Octonarii
1. iambic senarii: "six iambs" an iamb consists of a short then a long syllable. The Greek iambic trimeter consisted of three "metra" of two iambs each, in which the rules governing the first and second iamb of each pair were different. The Roman version is called iambic senarius because it had looser rules than its Greek predecessor. Iambic pentameter (based on wordaccent) is a very common meter in English:
The lády dóth protést too múch, methínks.
The first line of the Auluaria is a good example of iambic senarius:
ne quís mirétur quí sim // paúcis éloquár
The accent marks here indicate the second syllable of the iamb, not the accented syllable; but note that there is significant overlap between this iambic "ictus" and normal word accent.
Note that in this line there are exactly 12 syllables, but some of the iambs consist of two longs, rather than a single short followed by a long: all the syllables of "miretur" are long, the "i" by nature, the "u" by position. Also the last syllable of "paucis" is long.
Many lines of iambic senarius have more than twelve syllables by the process of substitution of two shorts for a long (General discussion of Meter #6). For example, in the second line of the prologue of the Aulularia, the first iamb consists of two shorts followed by a long. The same thing occurs in the same line with the words fámiliá and fámiliáris.