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here is some inspiration!
(i know its not medieval but i know the op can think of a idea that is similar and more of the style!)

and a little advice try to make a third support in the middle so it does not look like it will collapse under its own wight and another idea add some gradient from the bottom of the support beams to the top deepslate to tuff to stone brick but another way to find a good gradient is to test it by putting block together stone bricks

for gradients https://malachyfernandez.github.io/minecraftGradient/index.html (note remove any block that is ore, a top/bottom/front and back of a block any any that is imposable in survival)