Entry #4 - Bridges

The Maria Pia Bridge, a railway bridge built in 1877, is a beautiful example of a parabolic arch. As you can see, the arch spans across the length of the bridge, suspending it over the river. This is very common in bridge design, as the strength of the arch is very useful for holding not only the weight of the bridge, but the mass of the heavy trains and their cargo, or whomever else needs to use it. It's not exactly good for business if all the products you're transporting fall into the river Douro in transit due to the bridge collapsing, so arches are very necessary. Long live the parabolic arch!