At the Second Coming Christ will appear in the heavens, seated on a cloud and surrounded by the angelic hosts (Matthew 16:27; 24:30; 25:31)

The above picture very clearly shows Jesus stepping out of a portal with the "Host of Angels" still to come through.
 

Mathew 16:27. For the Son of man shall come in the glory of his Father with his angels: and then will he render to every man according to his works.
Filius enim hominis venturus est in gloria Patris sui cum angelis suis et tunc reddet unicuique secundum opus eius

Mathew 24:27. For as lightning cometh out of the east and appeareth even into the west: so shall also the coming of the Son of man be.
Sicut enim fulgur exit ab oriente et paret usque in occidente ita erit et adventus Filii hominis

Mathew 24:29. And immediately after the tribulation of those days, the sun shall be darkened and the moon shall not give her light and the stars shall fall from heaven and the powers of heaven shall be moved.*
Statim autem post tribulationem dierum illorum sol obscurabitur et luna non dabit lumen suum et stellae cadent de caelo et virtutes caelorum commovebuntur

Mathew 24:30. And then shall appear the sign of the Son of man in heaven. And then shall all tribes of the earth mourn: and they shall see the Son of man coming in the clouds of heaven with much power and majesty.*
Et tunc parebit signum Filii hominis in caelo et tunc plangent omnes tribus terrae et videbunt Filium hominis venientem in nubibus caeli cum virtute multa et maiestate

Source: Catholic Encyclopedia
 

Angels
from Catholic Encyclopedia:

(Latin angelus; Greek aggelos; from the Hebrew for "one going" or "one sent"; messenger). The word is used in Hebrew to denote indifferently either a divine or human messenger. The Septuagint renders it by aggelos which also has both significations. The Latin version, however, distinguishes the divine or spirit-messenger from the human, rendering the original in the one case by angelus and in the other by legatus or more generally by nuntius. In a few passages the Latin version is misleading, the word angelus being used where nuntius would have better expressed the meaning, e.g. Isaiah 18:2; 33:3, 6.

The angels are represented throughout the Bible as a body of spiritual beings intermediate between God and men: "You have made him (man) a little less than the angels" (Psalm 8:6). They, equally with man, are created beings; "praise ye Him, all His angels: praise ye Him, all His hosts . . . for He spoke and they were made. 

Sabaoth
from Catholic Encyclopedia:

(In Hebrew, plural form of "host" or "army"). The word is used almost exclusively in conjunction with the Divine name as a title of majesty: "the Lord of Hosts", or "the Lord God of Hosts". The origins and precise signification of the title are matters of more or less plausible conjecture. According to some scholars the "hosts" represent, at least primitively, the armies of Israel over whom Jehovah exercised a protecting influence. Others opine that the word refers to the hosts of heaven, the angels, and by metaphor to the stars and entire universe (cf. Genesis 2:1). In favour of the latter view is the fact that the title does not occur in the Pentateuch or Josue though the armies of Israel are often mentioned, while it is quite common in the prophetic writings where it would naturally have the more exalted and universal meaning.

The Greek cross within a circle (cruciform nimbus) is used only when portraying Christ. In the San Giovanni ceiling, notice that the figure of God is also in the shape of a Greek cross, within a circle. Both can be taken as an examples of squaring the circle. - Source - Dartmouth University
 

The Middle Ages saw numerous appearances of the vesica used as an aureole, a field of radiance surrounding the entire body, a sort of body halo surrounding holy figures. This use continued into the Renaissance. It is the most common use of the vesica as an art motif. Interpreting the aureole as a Venn diagram, it could represent the uniting of God and man or the intersection (crossroads [ed.]) of two realms, earthly and divine. - Source - Dartmouth University

Editors Note:

The depiction of the Halo around divine figures can be traced back to Buddhist traditions of the Aura that surrounds all beings. The more "spiritual" or divine the being, the larger and more golden is the aura. In Christian paintings and illuminations, this was known and depicted by the halo all around a deity. Later this was reduced to just around the head, and now in present day we see the halo as a mere circle above the head. This detracts from the real significance of the Halo/Aura. We will cover this topic in another paper.

Author Beth Vegh, in her series of E-books expressing her theory of Ancient  Star Gates she mentions the possible location of Eden being through a gateway in another realm. Looking at the picture below painted in 1445, it seems she is not the first to reach this startling conclusion.
 

The Earth (brown) at center, shown as a Mappamondo, or world map, surrounded by the three other elements, water, air, and fire, its bright red clearly marks the boundary between the sublunary and translunary realms. Then comes the moon and planets, all blue, except for the Sun, yellow-white, with gilded sunburst, and Mars, in pink, for the red planet. Then the fixed stars with signs of the zodiac, the Primum mobile (the first moved) which regulated the motion of all the spheres beneath it, and the Empyrean heaven, the home of God and the angels. - Source - Dartmouth University

In this painting the concept of passing through a portal to the Barren land of sand and rock where Adam and Eve were sent is very clearly portrayed.

A closer look around the edge shows that there are symbols around the 'gate'. There is one triangle marking top center on the inner ring but this may be a smudge of dirt, though I would wonder why they left it.
 

Mercury

Mercury Pope-Hennessy, John. Paradiso. The Illuminations of Dante's Divine Comedy by Giovanni di Paolo. NY: Random, 1993. p. 87