On April 21, 1915, came news of another trip to Warsaw by Zeppelins, a dozen persons being killed. Bombs fell in the center of the city and the post-office building was struck. A resumption of activity in that quarter was productive of raids, clashes in the air and Zeppelin alarms, such as were common in the western theatre, but on a lesser scale, as the Russians and Austrians possessed only a limited air equipment and the Germans were compelled to concentrate the bulk of their machines elsewhere. In the southern war zone the aerial operations recommenced with April, 1915. The Austrians made several more or less futile attacks on Venice. Italian cities, especially Venice, Verona, and others near the border removed many of their art works to safe places, including stained-glass windows from cathedrals, canvases, and statuary. The base of the Campanile, Venice, and other historic edifices were protected with thousands of sandbags. The famous horses brought from Constantinople were taken down. This denuding process robbed the ancient seat of Venetian power of its many splendors, but assured their preservation and future restoration. The Austrian bombs started numerous fires, tore up a few streets, and caused some casualties. In turn, the Italians dashed across the Austrian lines and attacked supply bases, railway stations, and other vantage points in the same way that the Allies were harrowing the Germans on the western front. In this work the Italians made use to some extent of their dirigibles, a type smaller than the Zeppelin but highly efficient. Thirty persons were killed or wounded in Calais on April 26, 1915, when a Zeppelin succeeded in reaching a point above one of the thickly populated sections of the city. The raid took place before midnight. The visitor was quickly driven away by a French machine, but not until the damage had been done. An orphanage was among the buildings struck, many of the victims being children. A fleet of aeroplanes visited Amiens at about the same hour, their efforts being directed to the bombardment of ammunition depots near that city. The invaders were driven off with small results to show for their work.