Andrei Rublev's icon of the Holy Trinity--also known as the Hospitality of Abraham--was painted in Russia in the early 15th century and is possibly the most popular icon in today's world; it speaks alike to Orthodox Christians, Western Christians, non-Christians, and folks with no religious affiliation whatever. I myself use it in prayer but I also sometimes get entranced with just looking at it and absorbing its visual beauty.

An element of the latter is the icon's underlying geometrical construction: the three angels representing the Father, Son, and Holy Spirit are arranged vis-a-vis each other, the table, and the elements in the background in such a way that several geometrical figures including a circle, a triangle, and a cross are easily defined. It is marvelous how well this is done, as can be seen in the above illustration, without making the whole composition seem contrived. (The illustration is part of a University of Toronto course taught by Jaroslav Skira.)

Some thoughts on the theological implications of these geometrical figures are found in an on-line essay by Soo-Young Kwon, excerpts of which are printed below.

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[The cross is defined by a vertical line connecting the tree, the halo of the central figure, the cup, and the small rectangle on the front of the table. It is defined horizontally by a line passing above the halos of the two outer figures and through the halo of the central figure.] God's love is Holy and Tri-hypostatic. And this love is suffering love...Christians usually think the suffering of the Cross was only an event of the man, Jesus Christ. If this is true, the suffering is just a man's martyrdom, not a universal event of salvation...the suffering of the Cross is an event of God as Trinity, not only an event of Jesus Christ. The Father suffers with the Son on the Cross.

This rectangular space [on the front of the table] speaks about the narrow road leading to the house of God. It is the road of suffering. This rectangle is a starting point for the mystical union with the Trinity.

The oneness and mutual love of the three persons...are strongly symbolized around an unseen circle...The visual theology of the icon...seems embedded in the "social" doctrine of the Trinity...The geometrical element of the composition, the circle in the icon, is speaking to us visually: God is sharing, self-giving, and solidarity.