Alekseevsky Ravelin

The Alekseevsky Ravelin is named after the grandfather of Anna Ioannovna, Tsar Alexei Mikhailovich. Construction of the ravelin from stone and brick began in 1733 and was completed by the end of that decade. The ravelin was reinforced with U-shaped structures in plan — half-counterguards connected to it by solid walls — traverses. Three gentle ramps led up to the fortification wall for raising artillery and ammunition. Gate passages were arranged in the facades. The Neva-facing facade of the bastion was clad with granite slabs according to the design of engineer R. R. Tomilov between 1787 and 1797. It was separated from the main part of the fortress by a moat filled with water, which was filled in at the end of the 19th century. Window and door openings existed only in the ravelin’s wall-walk walls. In 1787, the counterguard of the ravelin facing the Neva was clad with granite. 

In the 1730s, along the shoreline, the main rampart, designed by B.-Kh. Minikh, was connected to the ravelins by a system of botardo dams, which served as dams to maintain the necessary water level in the fortress’s moats and canal and prevented enemy ships from entering from outside. The walls of the botardo (the above-water part of the dam) were originally made of hewn slab stone; the underwater part of each dam consisted of two semicircular water gates, the upper parts of which are still visible today. In 1787, round turrets on the two southern botardos were clad with granite, and the wooden palisades were replaced with cast iron ones. The turrets on the northern botardo were covered with a slate slab in 1794. Between 1862 and 1865, their wooden palisades were also replaced with cast iron ones.

Almost from the very beginning, it was used to house political prisoners. In 1769, a wooden prison was built on the territory of the ravelin. In 1797, according to the design of architect P. Yu. Paton, a stone "Secret House" was built in its place — a place of confinement for the most dangerous political prisoners.  

More details about the prison of the Peter and Paul Fortress here: https://reveal.world/story/petropavlovskaya-krepost-glavnaya-tajnaya-tyur-ma-imperii

At the same time, fortification structures of the ravelin were dismantled to accommodate the buildings of the Military Ministry archives (only the escarp wall remains, heavily trimmed). In 1769, a wooden prison was built on the territory of the ravelin. During the investigation period, Decembrists P. I. Pestel, K. F. Ryleev, S. I. Muravyov-Apostol, S. G. Volkonsky, S. P. Trubetskoy, N. A. and M. A. Bestuzhev were held in 20 solitary stone cells; in 1849, members of M. V. Butashevich-Petrashevsky’s circle, including F. M. Dostoevsky; from 1862 to 1864, the ideological leader of revolutionary democracy N. G. Chernyshevsky. From 1882 to 1884, members of the "People’s Will" organization were held under penal servitude. The ravelin casemates served as barracks for guards. In 1893, the prison was demolished, the casemates dismantled, and the Military Ministry archives building with two service officers’ wings was built in their place. In 1892, the fortress water moat was filled in.

Sources:

http://www.world-art.ru/architecture/architecture.php?id=2552

https://www.spbmuseum.ru/themuseum/museum_complex/peterpaul_fortress/objects_fortress/alekseevskii_ravelin.php