A complete list of covered bridges in Michigan with pictures. These famous MI covered bridges are a favorite among historic architecture and bridge enthusiasts. A covered bridge is a bridge with sides and a roof. Since many bridges used to be made of wood, the earliest covered bridges were originally built in order to protect the bridge from the elements. The results were dramatic. Whereas a normal wooden bridge would only last for a decade, covered wooden bridges could last for up to a century. Historic preservationists have increased these bridges' longevity even further. Today, modern covered bridges are often built using metal and concrete, making their roof purely aesthetic. This list is comprised mostly of older, traditional covered bridges. Many of them have become important iconic landmarks for their region.