Not on display
As Federico Crimi and Ian Warrell have recognised, the subject is the Porta Ticinese,1 which stands on the south-western side of central Milan, facing the modern Piazza Ventiquattro Maggio. The free-standing Ionic neoclassical structure is shown from the south-east, with the arches of the further of its flanking pavilions beyond and the corner of the nearer to the right.
Crimi 2007, p.39 note 56, and undated note by Warrell in Tate catalogue files.
There is a prominent finger print at the bottom centre.