Sitting at the western edge of Guanabara Bay is Rio de Janeiro, a metropolis known throughout the world. On the eastern edge is Niterói, Rio's oft forgotten twin. Since 1613, the Santa Cruz fortress has gazed down upon any ship entering the bay. In colonial times it protected the city from pirates, and in 1894, its garrison foiled an attack by navy mutineers intent on ousting the president. Since 1846, the enormous Mauá shipyard has made Niterói the center of Brazilian shipbuilding. Over a century since its construction, none have surpassed its size. Niterói is prosperous, but its rapid growth has severely strained its infrastructure. Every day, more than 100,000 people travel between it and Rio by ferry. Anger at this expensive and unreliable service triggered a riot in 1959, leaving residents and officials to wonder if there is not a better way to connect the twin cities on the Guanabara.