To the north-west, Castro Pretorio borders with Sallustiano (R. XVII), from which is separated by Via XX Settembre, up to Porta Pia. To the north-east, Castro Pretorio borders with "Quartiere" Nomentano (Q. V), whose boundary is outlined by the stretch of the Aurelian Walls beside Viale del Policlinico, between Porta Pia and Viale Castro Pretorio and by a portion of the Viale itself.