system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did they build Medieval bridges in deep water?

I have only the barest understanding of how they do it NOW, but how did they do it when they were effectively hand laying bricks and what not? Did they have basic diving suits? Did they never put anything at the bottom of the body of water?
gpt
They built them in air, not underwater. First they blocked off the water around where they were going to dig and build using what are called Cofferdams or Caissons made of pile driven wood or stone and pumped out by bucket, dug the foundation and built to the water line and then removed the temporary structure. Pressurized versions are relatively new but can go deeper but the original idea is almost 2 millennia old and would have been used for major bridges during that time.