A reader asked why, as we see in some “Creation” icons,  Jesus as the Logos is depicted as creating while seated upon a circle — in short, what is the circle?

We find an example in the 12th century mosaics of Monreale, Palermo, Sicily:

The circle on which Jesus sits represents the throne of God:

Οὕτως λέγει Κύριος· ὁ οὐρανός μοι θρόνος, ἡ δὲ γῆ ὑποπόδιον τῶν ποδῶν μου·
“Thus says the Lord: Heaven is my throne, and earth a footstool for my feet.” (Isaiah 66:1, also Acts 7:49)

Κύριος ἐν ναῷ ἁγίῳ αὐτοῦ· Κύριος ἐν οὐρανῷ ὁ θρόνος αὐτοῦ.
The Lord is in his holy temple; the throne of the Lord is in Heaven.”
(Psalm 10:4 Septuagint numbering, 11:4 KJV)

ἐγὼ δὲ λέγω ὑμῖν μὴ ὀμόσαι ὅλως· μήτε ἐν τῷ οὐρανῷ, ὅτι θρόνος ἐστὶν τοῦ θεοῦ· μήτε ἐν τῇ γῇ, ὅτι ὑποπόδιόν ἐστιν τῶν ποδῶν αὐτοῦ·

“But I say to you, do not swear at all, neither by Heaven, which is the throne of God, nor by the earth, which is a footstool for his feet.” (Matthew 5:34-35)

Simultaneously, the circle depicts the heavenly realm in contrast to the earthly realm.  It is often composed of three concentric circles — as in the Monreale mosaics.  Some like to think of these as  symbolizing the three persons of the Trinity.  We might think of them as white for the Holy Spirit (the outer circle), blue for Jesus (the middle light blue circle), and the deepest blue circle for the Father, hidden in the darkness of Eternity.  That understanding may not fit all examples.