In the following centuries Moscow expanded rapidly outside the Kremlin walls and as Russia's borders became more and more secure their defensive duty has all but passed. The cannons which were installed in the walls were removed after the turn of the 17th century, as was the second, smaller wall which repeated the perimeter on the outside. During the reign of Czar Alexei Romanov, the towers were built up with decorative spires and the walls were restored. However their historical mightiness was dampened as the material became brick not stone. Successive restorations of varying scale took place during the reigns of Empress Elizabeth and Alexander the First as well as the later Soviet and Russian times, preserving their original character and style.