Note : Shelley’s note :

This poem was conceived and chiefly written in a wood that skirts the Arno, near Florence, and on a day when that tempestuous wind, whose temperature is at once mild and animating, was collecting the vapours which pour down the autumnal rains. They began, as I foresaw, at sunset with a violent tempest of hail and rain, attended by that magnificent thunder and lightning peculiar to the Cisalpine regions.

Maenad : follower of Dionysos (Bacchus), literally ‘mad woman’.

Pumice : a stone created by volcanic eruptions.

Baiæ : Shelley wrote to Peacock about his trip from Naples to the Bay of Baiæ, describing the sea as ‘so translucent that you could see the hollow caverns clothed with glaucous sea-moss, and the leaves and branches of those delicate weeds that pave the unequal bottom of the water.’ They sailed on, ‘passing the Bay of Baiae, and observing the ruins of its antique grandeur standing like rocks in the transparent sea under our boat.’5 (Letters) There are ruined Roman villas under the water at Baiae.

Shelley notes : The phenomenon alluded to at the conclusion of the third stanza is well known to naturalists. The vegetation at the bottom of the sea, of rivers, and of lakes, sympathises with that of the land in the change of seasons, and is consequently influenced by the winds which announce it.