Aventine Keyhole

The Priory of the Knights of Malta sits on the Aventine behind a green door, and looking through its keyhole shows St Peter's dome perfectly centred at the end of a hedged avenue in the garden. It is not an accident: Giovanni Battista Piranesi, better known as an engraver of Roman ruins, redesigned the priory and its square in 1765 and aligned the garden path to frame the dome. There is a further curiosity in that the view crosses three sovereignties at once, since the Order of Malta holds extraterritorial status. A queue forms most of the day, and photographing it well is difficult.

What you actually see

• The framed dome - St Peter's centred at the end of a hedged avenue.
• The Piranesi design - a square and priory laid out by the engraver in 1765.
• The three sovereignties - the sightline crossing Italy, the Order and the Vatican.
• The Aventine gardens - the orange garden and Santa Sabina nearby.

When to go

Year-round; early morning avoids the queue, which builds through the day and can run twenty minutes or more. The view is best in clear light with the dome lit.

Honest expectations

The queue is often long for a glance through a keyhole. Photographs through it are hard to take and rarely match what the eye sees. The priory garden itself is closed to the public.

Nearby

Santa Sabina and the orange garden are steps away; the Circus Maximus is below.