In Christian tradition even simple shapes are symbolically potent. A circle, for example, being without end, is a symbol of the divine; a triangle refers to the Trinity, a line, like the horizon, can mark out the bounday between heaven and earth, or between the sacred and the secular.

More Symbols of Christianity: 

Index of Christian Symbols

The Human Body as a Symbol of the Sacred
The body as a symbol of the sacred

The Face of Jesus as a Symbol of Faith
The Face of Jesus as a symbolic construct.

Pop Christianty
Pray, How Often? Pop culture and commerical images in service to the Christian faith ... or is it Christianity in service to commercialism? You decide.

The significance of color in Christian symbolism
The meaning of color in Christian symbolism

Food symbols in Christian tradition
Food symbols in Christian tradition

Doves, Eagles, and Sparrows
Doves, Eagles, and Sparrows ... birds as symbols of the divine.

Nature as a Source of Symbolism in Christianity

The Fish
The fish has been an important Christian symbol, not only because of the fact that Jesus included several fishermen in his close circle, but also because The initial letters of each word in the Greek phrase "Jesus Christ, Son of God, Savior" form the word ICHTHUS, which means "fish."

Christian ship symbols
Christian ship symbols

The Ankh Cross
The Ankh Cross is an ancient Egyptian symbol for life, combining the feminine circle and masculine staff to form the whole. It was adapted by early Christians because of its resemblance to the cross.

The Jerusalem Cross
Jerusalem Cross

The Maltese Cross
The Maltese Cross