Porta di Sant'Isaia does not exist any more. It used to stand on the crossing of the ring boulevard, Via Sant'Isaia and Via Andrea Costa. Compared with other gates, this gate had a short life. It was built only in 1568 to defend the opening in the Western part of the wall after the previous closing of the gate del Pratello (built in the 13th century and closed in 1445 after the assassination of Annibale I Bentivoglio). The gate Sant'Isaia stood on the road to Certosa (Bologna's cemetery) and to Porretta and Pistoia. It was demolished in 1903 after previous damages.
Source: "Restauro delle porte di Bologna 2007-2009"