The Moscow Kremlin and Red Square: Kremin Guide

      For firing on the enemy at different levels there were the loopholes of the so-called lower and upper firing tiers. If the enemy managed to reach the foot of the tower, the defenders made use of special loopholes or machicolations through which they tossed firebrands or boiling pitch.
      Adjoining the carriage-way towers were barbicans containing openings and apertures to hear what was going on outside the walls. From the gates of these barbicans drawbridges were lowered on chains over the moat. The gateway was fitted with a portcullis and strong doors bound with iron. If the enemy managed to break through the gate the portcullis was lowered and they found themselves in a trap fired on from above.
      The Kremlin was protected by water on all sides: on the south by the River Moskva, on the northwest (where the Alexandrovsky Gardens now are) by the River Neglinnaya, and on the east by the so-called Alevis artificial moat which was very deep. It was dug at the beginning of the sixteenth century and ran from the Corner Arsenal Tower along Red Square to the Beklemishev Tower, linking the Neglinnaya with the River Moskva.

All Saint's Brige and the Kremlin at the End of the 17th Century.
By Apollinary Vasnetsov, 1922.

      The Kremlin walls, following the relief of the terrain, were built in a slightly crooked, enabling the defenders of the fortress to fire on the enemy at close range. They were made of large well-baked bricks called "twohanders", because they were so heavy (about eight kilos each) the masons had to pick them up with both hands. The walls are 2,235 metres long, between 3.5 and 6.5 metres thick and from 5 to 19 metres high, depending on the relief. The firing platform which runs along the top, is from 2 to 2.5 metres wide. The walls are topped by merlons in the shape of swallow tails, characteristic of Italian fortresses. The merlons are from 2 to 2.5 metres high and not more than 70 centimetres thick. They have slit embrasures. During a siege the defenders covered the spaces between the merlons with boards.
      Running along the inside of the walls is the arcade which one finds in many Russian fortresses; the outer walls are decorated with a white-stone ornamental balister band.
      By the time the Kremlin building was completed there were many houses of traders and artisans clustered round its walls, which made the fortress easy to besiege and hampered its defence. For this reason in 1496 Ivan III ordered all the churches and houses to be removed from the Kremlin walls and forbade any construction within 220 metres of them. The buildings were removed from the River Neglinnaya side and from the east wall, where as a result of this a square appeared, later to be called Red (krasnaya or beautiful) Square. This act of Ivan Ill's was of artistic as well as defensive importance. Muscovites were now able to admire the main panorama of the Kremlin from Zamoskvorechiye (area over the Moskva River).
      As already mentioned, the Moscow Kremlin has twenty towers. The first to be built was the Secret Tower (1485) and the last the Tsar Tower (1680). We shall begin our description of the towers with the main one, the Saviour Tower, formerly called the Florus Tower after the Church of SS Flo-rus and Laurus which once stood nearby.