In the meantime, on the 18th October, a Russian field army was observed to be manœuvring on the allied flank and rear, and threatening the somewhat isolated garrison of Balaclava. The defensive measures taken for the defence of Balaclava consisted of inner and outer lines of defence. The town and harbour themselves were protected by steep hills, except at the gorge of Kadikoi, towards the north. Accordingly, these hills were fortified by the marine artillery, and held by marines and two companies of the 93rd regiment, while the gorge of Kadikoi itself was defended by six companies of the 93rd Highlanders and a battalion of Turks, with artillery, the whole constituting the inner line of defence. Now the gorge of Kadikoi opens out into a more or less level plain known as the plain of Balaclava, a mile north of the town. It was here that there was destined to be fought the great cavalry battle which holds so glorious a place in annals of the British army. Right across the centre of this plain, which is three miles long by two broad, and hemmed in on all sides by hills from 300 to 400 feet high, is a low continuous chain of hills or ridge dividing the plain of Balaclava into two portions, called respectively the north and south valleys, and carrying the main Woronzoff Road or Causeway. This ridge of hills was known to our men as the Causeway heights, and constituted the outer line of defence, by which the enemy might be hindered from even penetrating to the south valley. A chain of redoubts were thrown up along the Causeway heights by our engineers and manned by Turks. The only supporting force available in the event of an attack was the cavalry, under Lord Lucan, some 1500 strong, which was encamped in the south valley within the outer line of defence. The cavalry force consisted of two brigades--the Heavy Brigade, composed of the Scots Greys, Enniskillens, 1st Royal Dragoons, and 4th and 5th Dragoon Guards, under General Hon. James Scarlett, and the Light Brigade, under Lord Cardigan, consisting of the 4th and 13th Light Dragoons, the 8th and 11th Hussars, and the 17th Lancers. The whole garrison of Balaclava was, as before mentioned, under the chief command of Sir Colin Campbell.