The ground plan for St Isaac’s is Greek-cross with a superstructure surmounted with a large golden central dome and four subsidiary domes. The general design of the cathedral with the central dome later influenced the design of the Capitol Building in the American capital, Washington D.C. The exterior of the building is enriched by 112 columns of red granite, capped with Corinthian capitals. The interior features many columns, pilasters, and a floor made of multicolored granites and marbles with a sculptured dove, representing the Holy Spirit, suspended beneath the central dome. The iconostasis is built in a frame of eight stone columns. The entrance to the cathedral is through relief covered bronze doors patterned after the doors on the Battistero di San Giovanni in Florence, Italy.
Under the Bolshevik government, the parishioners and clergy attempted to cooperate in efforts to aid those in the countryside who, in 1921, were overcome by drought and famine. The Soviet government, however, requisitioned all divine service articles and, under a V. I. Lenin directive, all cathedrals were vandalized for their valuable furnishing and liturgical vessels. After the Church of Patriarch Tikhon and Metropolitan of Petrograd Benjamin was declared “counterrevolutionary” St. Isaac’s Cathedral was one of the 113 churches in St. Petersburg that was turned over to the “cooperating clergy” (the [[living church]], also renovated church). The “cooperating clergy” held the cathedral until it was closed in June 1928. In 1931, the cathedral was used as a museum of atheism until 1937 when it became a museum of history and art. The dove under the dome was removed and replaced by a Foucault pendulum as part of the conversion to a museum. During World War II the golden dome was painted over with grey paint to lessen its prominence as a geographical feature.
After the fall of the Soviet government, regular religious activities resumed in the cathedral on [[June 17]], 1990 with a divine liturgy served by Patriarch [[Alexei II (Ridiger) of Moscow|Alexei II of Moscow and All Russia]]. The museum was closed and, while the main altar area in the [[nave]] is now only used for major events including [[feast]]s, regular services are held in the chapel on the left side of the nave.