There are many kinds of bridges. Engineers design each type of bridge by knowing about forces.

The simplest kind of bridge is to put a slab of rock across two upright pieces of rock. Rock is strong and so will not break. This kind of bridge is called a clapper bridge. A modern form of this kind of bridge is a box girder bridge. They are very common.

Another thing you can do is to build brick or stone arches and put a flat surface across them. These are also common.

Another thing you can do is to suspend the surface, or deck, of the bridge from tall pillars, attaching the deck by wires suspended from the pillars. This is a suspension bridge.

You can lift bridge decks by pivoting them around a point and then applying a force on one end. Some raising bridges are famous, but raising bridges are the least common type.