Potemkin then embarked on a period of city-founding. Construction started at his first effort, Kherson, in 1778, as a base for a new Black Sea Fleet he intended to build. Potemkin approved every plan himself, but construction was slow, and the city proved costly and vulnerable to plague. Next was the port of Akhtiar, annexed with the Crimea, which became Sevastopol. Then he built Simferopol as the Crimean capital. His biggest failure, however, was his effort to build the city of Ekaterinoslav (lit. The glory of Catherine), now Dnipropetrovsk. The second most successful city of Potemkin's rule was Nikolayev (now better known as Mykolaiv), which he founded in 1789. Potemkin also initiated the redesign of Odessa after its capture from the Turks; it was to turn out to be the greatest.  Potemkin's Black Sea Fleet was a massive undertaking for its time. By 1787, the British ambassador reported twenty-seven battleships. It put Russia on a naval footing with Spain, though far behind the British Navy. The period represented the peak of Russia's naval power relative to other European states. Potemkin also rewarded hundreds of thousands of settlers who moved into his territories. It is estimated that by 1782 the populations of Novorossiya and Azov had doubled during a period of "exceptionally rapid" development. Immigrants included Russians, foreigners, British convicts diverted from Australia, Cossacks and controversially Jews. Though the immigrants were not always happy in their new surroundings, on at least one occasion Potemkin intervened directly to ensure families received the cattle to which they were entitled. Outside of Novorossiya he drew up the defensive Azov-Mozdok line, constructing forts at Georgievsk, Stavropol and elsewhere and ensured that the whole of the line was settled.  In 1784 Lanskoy died and Potemkin was needed at court to console the grieving Catherine. After Alexander Yermolov was installed as the new favorite in 1785, Catherine, Yermolov and Potemkin cruised the upper Volga. When Yermolov attempted to unseat Potemkin (and attracted support from Potemkin's critics), he found himself replaced by Count Alexander Dmitriev-Mamonov in the summer of 1786. Potemkin returned to the south, having arranged that Catherine would visit in the summer of 1787. She reached Kiev in late January, to travel down the Dnieper after the ice had melted (see Crimean journey of Catherine the Great). Potemkin had other lovers at this time, including a 'Countess' Sevres and a Naryshkina. Leaving in April, the royal party arrived in Kherson a month later. On visiting Sevastopol, Austria's Joseph II, who was traveling with them, was moved to note that "The Empress is totally ecstatic... Prince Potemkin is at the moment all-powerful".

Answer this question "What did Grigory Build?" by extracting the answer from the text above.
Construction started at his first effort, Kherson, in 1778, as a base for a new Black Sea Fleet he intended to build.