That is a perfect anchor for a story: you have a starting point in ancient reality, and an endpoint with the fact, that the trace of Alkimila's memory does persist, in the graffito. It's yours to fill in everything in between, which you've successfully done...
I like it when not too many "Romanisms" are put in the way of the progress of story-telling. Some stories place latin words for every little thing even when there's a completely suitable word in the writer's native language, and then seem more artificial than "authentic"...
You ideas are clearly good enough as well as your realization of them
Malta itself, is a good setting for such a story, with all its history, and the many traces of its existence under threat for centuries, that you can still find all over the island today.
The
devşirme (the systematic "collection" of Christian boys as living blood tribute, in order to be converted to Janissaries), and the sometimes upflaring resistance against it among the European peoples existing under Ottoman oppression, could be in itself a story source. Before technical advancements gave the West an advantage, Ottomans were only repelled where Europeans could bring themselves to equal or exceed them in brutality ... as seen in the example of the Siege of Malta... (or that certain famous Romanian dragon...) - the challenge for story-telling here will be, not to be carried away in a contest of escalating atrocities...