The smoke of the guns, drifting down on the land-breeze from the
summit of Mount Olia, now hid her white sails, now lifted and
revealed them in the late afternoon sunshine. But although blue held
the upper heavens--cloudless blue of July--the sunshine that reached
the ship was murky, almost copper-coloured; for it pierced through a
cloud of denser smoke that rolled continuously along the western
horizon from the burning houses of San Sebastian.

Sergeant Wilkes and his men, halting on the lower slope of the
mountain where it fell away in sand-dunes to the estuary of the
Urumea, had the whole flank of the fortress in view. Just now, at
half-tide, it rose straight out of the water on the farther bank--
a low, narrow-necked isthmus that at its seaward end climbed to a
cone-shaped rock four hundred feet high, crowned by a small castle.
This was the citadel. The town, through which alone it could be
taken by force, lay under it, across the neck of the isthmus; and
this again was protected on the landward side by a high rampart or
curtain, strengthened by a tall bastion in its centre and covered by
a regular hornwork pushed out from its front. So much for the
extremities, seaward and landward. That flank of the place which
it presented to the sandhills across the Urumea was clearly more
vulnerable, and yet not easily vulnerable. Deep water and natural
rock protected Mount Orgullo, the citadel hill. The sea-wall, for
almost half its length, formed but a _fausse braye_ for the hornwork
towering formidably behind it. Only where it covered the town, in
the space between citadel and hornwork, this wall became a simple
rampart; stout indeed and solid and twenty-seven feet high, with two
flanking towers for enfilading fire, besides a demi-bastion at the
Mount Orgullo end, yet offering the weak spot in the defences.