Austrian shell, Campiello Albrizzi, Venice
This morning I was exploring the area between San Aponal and San Polo, rightly described as a "succession of twisting alleys, dark corners and crumbling façades", in Ian Littlewood's book Venice: A Literary Companion.

I wandered down the aptly named Calle Streta, which is often held (erroneously) to be the narrowest alley in Venice, and soon found myself in the deserted Campiello Albrizzi. I immediately noticed, embedded in a wall, what I first took to be a conical-shaped hat, but which, on closer inspection, turned out to be a fragment of a shell. 

Underneath the shell was an inscription, written by none other than Gabriele d'Annunzio, poet, playwright and soldier. Littlewood provides the following translation: 

"This fragment of barbarism is lodged in the noble stone as testimony of the perpetual enmity which adds shame to their shame, glory to our glory. 10 August 1916."

The unnamed enemy were the Austrians.