When we think of these sieges, we can perhaps understand better why Gibraltar, rather than any of the other four towns, holds the key to the Strait. When our fleet was away the fortress was powerless and the enemy could close the passage. A fleet alone could keep it open, but a fleet, now as then, must have a harbour close at hand as a base. In the case of Gibraltar only of the five towns do we find both fortress and fleet together. The history of Gibraltar in the nineteenth century has been mainly concerned with the difficulties of governing its miscellaneous population and the problem of improving the defences and adapting them to the ever-changing conditions of modern warfare. Towards the end of the century the need of further dock accommodation for the fleet became pressing. The new harbour was begun in 1893, but while it was in course of construction the science of artillery was also making great progress, and it has been pointed out that the docks could be assailed by the fire from long-range guns hidden behind the hills on the mainland. So from the purely military point of view the fortress is perhaps less impregnable than in former times. In the matter of internal administration there has been much improvement. Gibraltar has gained a bad reputation in the past for climate and health. The bare rock adds to the burning heat of the summer sun; the town is shut off from fresh breezes by the hill, and when the Levanter blows from the east, and heavy clouds hang over the summit of the ridge, the clammy air makes the heat still more oppressive. There have been severe epidemics on the Rock, due largely to the bad drainage of the old town and the want of sufficient water. Most of the rain falls in the winter months, and a heavy downpour is soaked up at once by the porous rock. There are no springs, so the water is collected in tanks from the roofs of the houses, while the authorities have built reservoirs and artificial catches on the lower hill slopes and have set up condensing engines as a reserve in time of need. 14 Here is one of these catches on the north peak above Catalan Bay; it is made of sheets of corrugated iron, coated with cement, and lies like a roof over the porous sand beneath. There are wells, too, on the low ground to the north; but the water is brackish and not good for drinking. Better drainage and more water have greatly changed the condition of the town; so that the water famines and epidemics of the past are not likely to recur; but food must always be imported, as there is no room to grow it on the Rock, with its small area and poor soil.