The Eastern Orthodox Cross has three cross beams and is distinctly different from other Christian crosses.
The deep symbolism and the tradition of icons was preserved from Byzantium through the Christian Empire it created in Russia. (See also the heraldic Bezant Cross). Byzantium was the capital of the Christian Byzantine Empire, later renamed Constantinople and currently Istanbul. The culture of the area is a rich mixture of different traditions of iconography.
Alexander Roman tells us that in the East, and Russia in particular, a cross with three bars was worn by the lowest rank of priest; a privilege granted by the Russian Emperor Paul I (1754-1801). Higher ranking clergy wore one-bar crosses, such as Metropolitans and Abbots. In the West, the reverse was true - additional bars signified higher clerical or other significance. Two-bar crosses in the West signified important Christian centres, i.e., patriarchal centres. Only the pope had a three-bar Cross. (See also Papal Cross)
The top beam, also seen on the Patriarchal cross, represents the plaque bearing Pontius Pilate's inscription "Jesus the Nazorean, King of the Jews" (see INRI). The Latin for such a plaque is titulus which gives the name for this form: Titulus Cross. The upper beam rarely has any inscription; it is just symbolic of a titulus. However, this cross is often embellished with the acronym IC XC NIKA. (See also ICXC Cross)
The lower beam represents a foot-support (suppedaneum) and began appearing in Eastern Christian art in the 6th century. The purpose of the suppedaneum was to support the weight of the body. We do not know whether such a device existed on Jesus' cross. (See Suppedaneum Cross)
The suppedaneum on crosses typical of the Greek Orthodox Church1 and Ukrainian Catholic Church is invariably horizontal, whereas on other Eastern crosses it is usually diagonal.
A popular interpretation for the slanted suppedaneum is to symbolize a balance-scale showing the good thief St. Dismas, having accepted Christ, would ascend to heaven, while the thief who mocked Jesus would descend to hell. With this, the Cross is a balance-scale of justice. A similar lower beam is also found on another form of Patriarchal Cross where there is only one upper beam.
Another explanation of the slant reflects half of the 'X' shaped Saltire cross of St. Andrew, who was the first Christian missionary to Russia.
The story goes that when Andrew preached in southern Russia, he used a large three-bar cross as a visual teaching aid. All three bars were parallel, and when relating the Passion he tilted the lower footrest to signify that those on the right side of Christ will rise up into heaven and those on the left will slide down into hell. (See also Keys to heaven and Right-hand side of God.)
When first encountering this cross with a slanting lower beam, one can be forgiven for thinking the the Eastern Orthodox Cross is a Three-Dimensional Cross; its similarity with a key being a convenient reminder that the cross is the key to forgiveness. Three dimensions also brings to mind the Holy Trinity.