During the night Mexicans in the rear did some shooting but without effect, and the process of investment began. Diverting attention from this by having a gunboat, sheltered about a mile from the city behind Point Hornos, throw shot and shell into Vera Cruz for a couple of hours the next forenoon, Scott had Pillow's brigade capture the hill of Malibrán behind Worth's camp, and push on toward the rear of the city. Quitman then passed it; Shields passed Quitman, and Twiggs passed him. Wallowing up and down the slopes of deep sand in a sultry heat without water to drink proved to be extremely hard work; and breaking through the valleys, where a matted growth of chaparral--armed with thorns as keen as needles and stiff as bayonets--resisted everything but sharp steel, was harder yet. Day and night Mexican irregulars, both infantry and horse, and cannon salutes from the city and the castle embarrassed operations, and there were many brisk skirmishes. Moreover the landing had scarcely been made when a norther set in, covering the men with sand, blowing away old hilltops and building up new ones. But not long after noon on March 13 Twiggs reached the Gulf north of the city. The next morning a well-supported detachment from each brigade advanced as far as it could find cover, driving the Mexican outposts before it; and by night these detachments were only about seven hundred yards from the town.[22.21] The American position as a whole, known as Camp Washington, was now a semi-circular line about seven miles long. There were gaps, but these were rapidly closed with strong pickets. The railway and the roads were all occupied; the visible water supply of the city was cut off; and on March 16 Scott announced that nothing less than a small army could break through. Meantime, whenever the weather permitted, artillery, stores, horses and provisions were landed in the most systematic manner. Safeguards were issued to the representatives of foreign powers at Vera Cruz, and in a letter of March 13 to the Spanish consul[22.18] Scott indicated plainly that "bombardment or cannonade, or assault, or all" of these might be expected by the citizens.[22.21] The time to plant artillery had now arrived, and the ideal spot was found on the sixteenth; but after a battery had been laid out there, access to it proved to be dangerously exposed. Two days later, however, a fairly good point was discovered, near the cemetery and Worth's position, about half a mile south of the town, which screened it somewhat from the castle; and preparations to establish two mortar batteries there, about one hundred yards apart, began the following night. At the same time a deep road, wide enough to admit a six-mule team, was under construction.[22.21] [Illustration: SIEGE OF VERA CRUZ AMERICAN BATTERIES]