I'm writing a story set in ancient Greece. The protag has a sword. But it's not just any sword! The blade is leaf-shaped and roughly 25 inches in length; the handle is embossed with a cross-guard. It's not a sword but a xiphos (pron. "zifos"), an Iron Age Greek short-sword, and it's presented to him by his adoptive step-father as a present when he finishes his training. It looks something like this:
Very few xiphoi seem to have survived, but there are still xiphoi from as long ago as the late second millennium BC.
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I did much more research about these swords; the above is just a short excerpt. But it gave me a mental picture of what tools my protag would have had to fight or defend himself with. Then I did some research on what clothes he would have, what food he could eat, how he could travel etc. It gave me a picture of how he lived and what he would have looked like.
'The past is a foreign country. They do things differently there.' --L. P. Hartley, "The Go-Between" (1953)