This is the fourth in the sequence of views of Caernarvon Castle that Turner made in this book; the others are on the versos of folios 21, 22, 23, 25 and 26 (D01941, D01943, D01945, D01949, D01951). The sketch on D01949 is the abandoned beginning of a subject very close to this one. Another study, showing the towers wreathed in fantastical clouds, is folio 5 verso (D01917).
Here Turner’s boat, having brought him round the Caernarvon peninsular from the Menai Strait, has turned in to the harbour in the estuary of the River Seiont and he makes a summary sketch of the walls towering above the shipping. The name Seiont derives from that of the Roman fort, Segontium, which had been built on the river bank.