Bill Roan was working as a blacksmith when he decided that the Bay Bridge needed a guardian. He welded the original troll figure from steel and attached it to a structural element of the old eastern span, where it perched unseen by most commuters but visible to anyone who knew where to look. The figure was small -- about 18 inches tall -- and positioned in a spot that required searching to find. It was unofficial public art in the purest sense: unauthorized, unsigned for years, and created not for an audience but for the bridge itself.

Trolls guarding bridges is one of the oldest motifs in human storytelling, from Norse mythology to fairy tales. Roan's troll connected the Bay Bridge to this ancient tradition, transforming a piece of 20th-century infrastructure into something with mythological resonance. The troll became one of the Bay Area's most beloved pieces of hidden art, a secret that locals shared with visitors and that journalists periodically rediscovered. When the old eastern span was demolished, the question of what would happen to the troll generated genuine public concern.

Roan created a replacement troll for the new eastern span, which opened in 2013. The new figure maintains the tradition while adapting to the new bridge's design. Finding it remains a challenge for the curious -- the bridge is not a pedestrian-friendly environment, and Caltrans does not publicize the troll's exact location. This obscurity is fitting. A bridge troll that everyone could see would not be a proper troll at all. The Bay Bridge Troll works as art precisely because it operates at the edge of visibility, a tiny steel guardian that most people will never notice but that changes the bridge forever once you know it is there.