I took some reference shots and posed some models in Daz 3D to get them just so, and I was fairly happy with the characters. My first pass at the background, however, was not so great. The vertical columns are way too static and straight in contrast to the diagonal, flowing foreground action. With some great suggestions from my illustration colleagues I ditched this background and attempted a new, more dynamic composition.
The problem is that working with biologists and engineers for so long has the left-brained science nerd inside me yelling "No, no, no; Greek stone columns weren't designed to sustain an off-vertical angle; they would collapse under their own weight with unbuttressed support." So my right-brained artist is going "Shut up, science nerd. I just drew a woman with living snake hair; I don't need an engineering lesson. Give me your lunch money."
The new background silhouette, sketched digitally, turned out way better. I'm going to print this, break out the tracing paper, and pencil in some ruins.