The specific source I'm talking about is incredibly obscure: It's a possible fragment of Callimachus preserved by some grammarian talking about galliambic verse, an ancient meter related to the gallae. Here's an online version; it really doesn't say much. But better known is Catullus 63, a poem in galliambic verse about Attis, the consort of Cybele, and the gallae. (And it really does write "gallae", which I totally forgot about!) If you can stand some literally ancient transphobia, it's a nice read. There's also some interesting playing with grammatical gender in the Latin, even if it's all ultimately written from a reactionary position. It's a testament to transfemininity in Ancient Rome in any case.