I will also add that these things didn't just pop up from day one fully formed. No one's first ship was a tessarakonter. They would have started with some proto-ships, basically anything that could float, and overtime learn what makes the best floating stuff, perfect it, build upon it, etc.

Same with bridges, no one's building the Golden Gate on their first attempt. Early ones would have been very temporary, and quite even just "well we can walk across that spot that has a tree down, so why not just bring a tree down ourselves here?" Overtime you can learn to make them stronger, to bring more supplies over, to bring more people over, and eventually you might say "hey, we cross over this exact spot 7 times a week, but we're always replacing this wood, what else can we do here?"

While it would be mistaken to try and understand technology in a technology tree sort of way where it's all linear and constantly improving upon itself, especially in these prehistorical and ancient history societies, it might be okay to sorta imagine it like that if it helps gain a wider understanding. Better bridges required a better understanding of things like maths, physics, etc. Combining the understanding of building materials, purpose, arches, over time throughout many generations. The more a society grew, the more information they learnt, the better things could potentially be.