Porta San Mamolo is no more existing, it was destroyed with the wall in 1903. The gate was built in the 12th century and rebuilt several times. A drawbridge over the moat was added in 1334. A new keep was built in 1417. Despite its full restoration in 1850, the gate was demolished in the fever of “progress”.
Source: "Restauro delle porte di Bologna 2007-2009"