After the Italians had established their hold upon the frontier points there was an apparent relaxation of effort while the infantry of the line waited for the heavy siege artillery to issue from the armament factories and come into action. This movement of artillery was slow, especially on the Isonzo front where engineering operations were delayed by the summer floods caused by the melting snows from the mountain tops. To transport heavy pieces of ordnance across the floods the Italian engineers had to build strong bridges, often under heavy fire from the enemy, who, even after their retirement from the east bank of the river, continually harassed the Italian advance guard holding the bridgeheads. The Austrians aided the work of the mountain floods by breaking down the high embankment used to carry off the snow water, and thereby inundated the plain. Working under a plunging fire from the enemy's batteries on the foothills, the Italian sappers built light pontoon bridges over the floods upon which the first Italian contingent crossed at night and occupied the first line of Austrian trenches near the river. This much the Italians accomplished by the first week in June, 1915; but there they were forced to pause for the reasons already described. Active hostilities during the first part of June on the Isonzo front centered around Monfalcone, a seaport just below the dominating Carso headlands. Taken from Venice by the Austrians during the Napoleonic era, Monfalcone had become the third most important port in the empire. In its yards warships were being constructed. On June 9, 1915, the Italians made their swift stroke in a southwesterly direction from their Isonzo line. The port was bombarded on June 7, 1915, by a light Italian cruiser squadron, and the Castle of Duino, standing at the sea edge near Trieste and defended by three artillery batteries, was shattered and set afire apparently to prepare for the operations against Monfalcone from the southwestern side of the Gulf of Panzano. Archduke Eugene hastily collected a strong force above Duino ready to resist an attempt by the Italians to land, but the attempt never was made. It developed that the bombardment of Duino was a feint.