Borisoglebskaya Tower is a tower of the Nizhny Novgorod Kremlin, built in the 1970s on the site of the tower of the same name, which was dismantled 200 years earlier. It is located between the Zachatyevskaya and Georgievskaya towers.

The tower dates back to the 16th century. It was rebuilt in 1620. At that time, buttresses were added to the tower, in which casemates with loopholes were arranged. It was named after the nearby Church of Boris and Gleb (which has not survived). Another name is Dukhovskaya, after the nearby Holy Spirit Monastery (which has not survived).

In 1785, as a result of a landslide that destroyed the Borisoglebskaya and Zachatyevskaya towers, the latter, along with the adjoining curtain walls, were dismantled and replaced with lower walls. In 1833, the wall was rebuilt. Near the former Borisoglebskaya Tower, the "Dukhovskoy Prolaz" passage was arranged. The remains of the tower (part of the first tier) were excavated in 1966. In 1974, the tower was rebuilt on its original site.

In terms of plan dimensions, Borisoglebskaya Tower is closest to the round towers — Kladovaya and Porokhovaya; the thickness of the walls and the arrangement of the fighting niches in the curtain walls indicate a similarity in the internal layout of the first tier of all three towers. But unlike the other two, Borisoglebskaya Tower is located at the bend of the direction of the adjacent curtains, so to eliminate dead space in the base firing zone, a fighting niche was necessary.

Like all other round towers, Borisoglebskaya had four tiers. The second tier could only be similar in layout to the first and, like it, was covered with a dome vault (mentioned in the 1765 inventory). This determines the height of the tier, which is limited from above by the floor of the third tier, located at the level of the wall’s fighting gallery at the tower. Above the fighting gallery, its cylindrical volume was cut off by a vertical plane along the line of the crenellation wall. The third tier had thinner walls and a flat ceiling laid on the wall edge between the third and fourth tiers. According to calculations, the upper firing zone housed 8 large firing windows on the field-facing part of the tower and 3 windows on its inner wall. Thus, the upper platform was surrounded by 11 merlons, which are indicated in the Census Book.

The reconstruction of the internal layout and the calculation of the height dimensions of Borisoglebskaya Tower show that it was built similarly to the other round towers of the Nizhny Novgorod Kremlin.

Sources:

S. L. Agafonov. "Nizhny Novgorod Kremlin. Architecture, History, Restoration"

https://ru.wikipedia.org/wiki/Borisoglebskaya_Tower_(Nizhny_Novgorod)