Through arch bridge

Imagine you are playing with some toys, and you have two blocks that are kind of curved, with a dip in the middle. If you put them next to each other with their dips facing each other, you can make a bridge.

Now imagine you have lots and lots of those blocks, and you want to make a really big bridge that goes over a river or a valley. You start by putting two blocks down as your foundations, one on each side of the river. You then start building up from those blocks, placing more and more blocks on top of each other, making sure they're all touching each other and not falling over.

When you get to the top of the bridge, you still need more blocks to go across the gap between the two foundation blocks. This is where your curved blocks come in - you lay them on their sides between the two foundation blocks, with their dips facing each other. You keep adding more and more curved blocks until you have a nice smooth curve going across the gap.

The reason this works is because the curved blocks are really strong when they're under pressure from above - this is called compression. They can handle lots of weight pushing down on them without breaking. When you put lots of curved blocks together, they all help to support each other under this pressure.

So, when you put lots of curved blocks together in a line, you can make a really strong, smooth bridge that can handle lots of weight and still stay standing. This is called an arch bridge!