In 1557, however, a great flood caused the Tiber to change its course, so that it no longer flowed under the walls of the castle, but some half a mile farther west; and its old bed (Fiume Morto) has ever since then served as a breeding ground for the malarial mosquito (Anopheles claviger).
The harbour consisted of the outer basin, or Porto di Miseno, protected by moles, of which remains still exist, and the present Mare Morto, separated from it by a comparatively modern embankment.
The beaches which had been selected were, enumerating from right to left, " S " in Morto Bay, " V " and " W " on either side of Cape Helles at the south-western end, and " X " and " Y " on the outer shore; " V " and " W " were regarded as of primary importance, as those two beaches offered suitable landing places from the point of view of subsequent operations.
On the 27th a general move forward took place, the Turks (9th Div.) offering little opposition, and by nightfall the Allies held a line stretching approximately from the north end of Morto Bay to " Gully " beach.