After Russia's loss in the Crimean war in 1856 Russia was forbidden to have any warships in the Black Sea by Treaty of Paris, leaving one of the most important parts of Russia - its only non-freezing sea ports and the area through which most of Russia's sea trade went, unprotected. Hence in the late-1860s Russia started to think about abrogating the terms of the treaty in order to protect its coast against rapidly deteriorating relations with Turkey. It was obvious that in the beginning the strategy for the Russian fleet would be purely defensive against relatively powerful Turkish fleet and so in the 1869 it was decided to build armored warships to protect the coast and the ports. This where the Rear-Admiral Popov comes in, in the 1860s he was the unofficial head of the shipbuilding in Russia.
It was during the design discussions, Popov suggested an idea that he had for a while - building round ships which would have carried heavy armor and armament on smallest draft and displacement. To prove the concept a small round steam launch with a diameter 3.35m was built. It proved successful enough for the construction of the full size ships to proceed. In 1871 with the defeat of France in the Franco-Prussian was Russia denounced the Treaty or paris and set about restoring it's Black Sea fleet.
Initially 6 round ships were planned, but to begin with two were laid down in St. Petersburg in the beginning of 1871. If you are thinking that this sounds wrong as St. Petersburg is on the wrong sea, you are correct, but since the south of Russia was really underdeveloped in those years the ship hulls had to be laid down and built in St. Petersburg, then disassembled, shipped to the Black Sea port of Nikolaev in pieces, and then assembled again. This caused the immeasurable delays as the railroad to Nikolaev was only completed in the middle of the construction and sometimes reached absurdity, when it proved easier and cheaper to buy Russian wood in England and have it delivered to Nikolaev, rather than to ship it from the interior of the country. Nonetheless the construction of the first ship, called Novgorod, started on 17 December 1871, while the second one, Kiev, was laid down in January 1872. Novgorod's construction proceeded relatively smoothly but Kiev became a platform for Popov's experiments - new, lighter engines were ordered for it, armament and armor was increased and in the end the construction was stopped to await testing results of the first ship. Due to a bad financial situation in Russia at the time the other four ships were at first postponed and then cancelled all together.
Due to various delays in supplying the materials Novgorod was launched only on 21 May 1873. The ship was perfectly round with a diameter of 30.78m and displaced 2490 tons. It was armored with 9" upper and 7" lower belts and 1" armored deck. In the central circular barbette, armored with 9" armor, the ship carried two 26-ton 11" guns. The machinery arrangement was unusual, ship had six boilers and six engines arranged perpendicularly in the hull making 3360hp, each engine turning it's own screw. Three days after launch the sea trials of Novgorod began, during which it was determined that the top speed of the ship is 7 knots, which, as Popov triumphantly put in his message to headquarters, was equivalent to the speed of the other coast defense ships in the Russian navy at the time. Soon afterward the guns were installed. The gunnery trials showed a low rate of fire of 12-13 minutes per shot (which was also comparable to the other warships of the time), a maximum range of 4200m at the maximum elevation of 14.5 degrees and the ability to pierce 11" of armor at 730m. It was during the gunnery trials a legend about these ships was born - the guns on the Novgorod were installed on a circular track and the trials showed that the brakes that fixed the guns into position were too weak and during the shot they rotated on the track. The brakes were fixed but the legend mutated into the rumor the entire ship rotated during shooting and persists to this day. Initially there was no aft superstructure on the ship only a light deck aft of the barbette with a steering wheel, but based on the sea trials a real superstructure with an enclosed bridge was added. Overall the trials, predictably, showed that the ship had problems going against the waves since it's low speed became even lower, but at the same time could ride out even a heavy storm with only light rolling.
The construction of the second ship was stopped in mid 1872 and the redesign work only resumed after the trials of Novgorod in August 1873 with what was called in the report by Admiral Popov "some changes shown by tests". In reality what was supposed to be a sister ship to Novgorod, became a completely different ship. The ship was actually 6m bigger in diameter, becoming 36.57m, which necessitated the disassembly of the already built components. The armament was increased to two 12" guns and the maximum thickness of armor was increased to 18". On 13 August tsar Alexandr II allowed the construction of the redesigned ship and in October the ship was renamed Vitse-Admiral Popov in honor of its designer. The actual work started only in the spring of 1874 while the ship was officially laid down on 27 August 1874. The work was constantly interrupted by the problems with the delivery of parts. The ship was launched on 25 Sept 1875. The general layout of the ship was the same as the first popovka, but with everything being bigger. The main belt and the barbette armor was now composed of two layers - a 9" and a 7" layer. The ship had an amazing 8 engines and 12 boilers, making 4480hp, driving six screws (two inner screws were driven by two engines each). The armament consisted of two 12" disappearing guns and four 87mm light guns in the side sponsons. Because of the expected war with Turkey the main guns were installed on the temporary mountings which were too weak for them, while the proper mounts were being made. To improve the sea keeping the main superstructure was increased in size and resembled the hull of the normal ship. The ship reached 8 knots during trials, and was 1.75 knots faster than Novgorod at full speed. During the comparative trials between these two ships it was noticed that the outer screws were not effective and with only four screws the speed was only about half a knot less on either ships, the the outer engines and screws were removed to save weight, space and money. After the removal of the outer engines Novgorod's engines made a total of 2000hp while Popov's 3066hp.