In the XVI century Moscow began to strengthen their defensive positions. Around the capital city there is a number of fortresses, among which the Holy Trinity monastery. Wall Lavra was intended to protect the approaches to Moscow from the North-East side.

In 1540 began construction of a massive stone fortress. Ivan the terrible himself followed the progress of the work. He had allocated huge for those times money. An order was issued to use in the right amount of brick and mortar, and all that is needed. Built the walls of the peasants, the king exempted from all taxes and duties, even in difficult times. The Trinity-Sergius Lavra in the last ten years has become a powerful defense of Moscow Principality.

In 1608-1610, the glorious fortress was during the siege of Hetman Sapieha and Lisowski. Year, three months and twenty days the monks defended their positions without the help of the army. 15-thousand enemy troops were standing by the walls of the monastery, tried to storm the fortress, but the monks and district farmers even defended the bombing of 60 guns. Walls of red brick in the construction of intentionally bleaching to blows guns could not see the gaps. When the poles began to lead the saps, Nikon Shilov and Slots — the defenders of the monastery — climbed into one of these holes and blew it up with him. Superior forces of the Polish army retreated, and the courage and the will of the defenders of the Holy land inspired the liberation of Moscow. After this siege in the middle of XVII century the fortress wall was built up and expanded.

Now the length of the wall of the fortress is about 1200 m. Its wall thickness in some places up to 10 meters, and the height varies from 7 to 15 metres. Four towers at the corners of an irregular quadrangle and seven on the walls were used for additional protection. Calicia not intended for defence, and served as the entryway for pilgrims. The name says about it. Over the Holy Gates – the main entrance to the monastery is the Red tower. In 1856 appeared over the gate portal with beautiful moldings and the image of the Holy Trinity from the Ural stones, and the tower itself has acquired a semi-circular dome with an onion dome. In the North-Eastern corner of the fortress is Atocha tower (formerly Sitnicka), which acquired its current name because of the white stone carving of the duck, decorating the top. She and two corner towers have a polyhedral shape, and the tower above the Water gates against Atocha "quadrangular". Scientists believe that all the corner towers in the sixteenth century had an underground tiers. The most beautiful think Beer tower, standing at the Western wall on a steep slope. Its height of almost 20 m. This is the largest of prasalnik towers. Only in it there are four tiers instead of three, as in the rest of. Thanks to ten differential land inside and outside of the tower and broad goal, misleading, she served as a stone bag for the enemy and convenient access for the monks. Pyatnitskaya tower see residents and visitors from Sergiyev Posad, being on the lookout Pancake Mountain.

The walls between the towers have three combat tier. Bottom is for "foot fight" and consists of open from the laurels arcade. Above – average fight in the form of a vaulted gallery with loopholes and top outdoor tier with scalloped edge. The gallery was allowed to go around the monastery wall. This added maneuverability during combat. The inventory of 1641 States that the monastery was kept on the walls of 90 guns, and 20 were in reserve.

The moat surrounding the monastery, served as an additional obstacle to the enemy. In order to increase the impregnability of the fortress walls, dams were built, and on the South side you can admire huge the Taylor's pond, arranged in 1552 and decorating Sergiev Posad still.