Hence such passes should only be considered as fixed points, around which an army should operate freely in defence of more exposed positions, for defiles are doors, the keys of which are on the summits of the hills around them. A bridge is a defile, yet troops are posted, not in the middle, but behind a bridge, to defend the passage. By extending this principle, we shall draw the greatest advantages from the strength of mountain-passes. The practice of some great generals may, indeed, be quoted against this opinion; nevertheless, it seems more consonant to the true principles of war to place detachments in defiles, and keep the main body in some central point behind, ready to fall on the heads of the enemy’s columns as they issue from the gorges of the hills. Pierced by many roads, and defended by feeble dispirited troops, the Morena presented no great obstacle to the French; but, as they came up against it by the way of La Mancha only, there were means to render their passage difficult. If Albuquerque, placing his army either at Almaden de Azogues, or Agudo, had operated against their right flank, he must have been beaten, or masked by a strong detachment, before Areizaga could have been attacked. Nor was Andalusia itself deficient of interior local resources for an obstinate defence. Parallel to the Morena, and at the distance of about a hundred miles, the Sierra Nevada, the Apulxaras, and the Sierra Ronda, extend from the borders of Murcia to Gibraltar, cutting off a narrow tract of country along the coast of the Mediterranean: and the intermediate space between these sierras and the Morena is broken by less extensive ridges, forming valleys which, gradually descending and widening, are finally lost in the open country about Seville. Andalusia may therefore be considered as presenting three grand divisions of country:--1º. The upper, or rugged, between the Sierra Morena and the Sierra Nevada. 2º. The lower, or open country, about Seville. 3º. The coast-tract between the Nevada and Ronda, and the Mediterranean. This last is studded, in its whole length, with sea-port towns and castles, such as Malaga, Velez-Malaga, Motril, Ardra, Marbella, Estipona, and an infinity of smaller places. [Illustration: _Vol. 3, Plate 4._ INVASION of ANDALUSIA 1810. _Published by T. & W. Boone, 1830._]