Complex sentence: Originally this was an ancient Roman stone bridge with three arches, which unfortunately was destroyed during World War II. The new bridge, rebuilt in 1953 in concrete, has only a single arch, the design being intended to reduce the risk of flooding.
Split into simpler sentences: Originally this was an ancient Roman stone bridge with three arches. It was destroyed during World War II. The new bridge, rebuilt in 1953 in concrete, has only a single arch, the design being intended to reduce the risk of flooding.