One of the central and most notable features of nearly every Orthodox church is the iconostasis (all, save the Western Rite parishes). “Iconostasis”—simply “iconostas” among Slavs—means nothing more than “icon stand,” and it separates the nave from the sanctuary and altar. It may consist of icons set up on two easels in a mission church, or be as large as a gigantic wall with dozens of icons and three doorways.
The iconstasis developed over time, but it is not without precedent in antiquity. Recent archaeological evidence suggests that certain groups of ancient Jews decorated their synagogues with icons depicting biblical figures and events, and in at least one archaeological excavation, there is a full wall of icons separating the gathering room from a sort of Torah shrine.
Around the 5th century, it became customary in eastern churches to construct a templon between the nave and altar. In the west, a similar development occurred with a “rood screen.” Over time, these elements came to be adorned with icons, and eventually became what we know as the iconostasis. There are many variations in these icon stands, but the general set-up is guided by Church rubrics, and so several features are fairly common. (And despite many years of separation from the mainstream Chalcedonian Orthodox Church, even some of the so-called “Oriental Orthodox” churches, especially the Coptic Orthodox, have embraced the iconostasis.)
Beyond the basics, liturgically, the iconostasis is equipped with three important entrances: two “deacon” doors, and one central entrance. Anyone with a blessing from the bishop (or by proxy, the priest) can enter the deacon doors, but only ordained clergy (bishop, priest, or deacon) may enter the central doors. In churches where there are several deacons, these doors are used frequently in services, and it’s hard not to imagine the workings of a cuckoo clock! These deacon doors are typically adorned with icons of deacons or archangels (and are sometimes called “angel doors” due to the icons of Archangels Michael and Gabriel).
The middle entrance usually consists of two doors, sometimes called the Royal Doors or Beautiful Gates, and a curtain. This doorway is used exclusively by clergy for liturgical purposes. These two doors are frequently adorned with icons of the four evangelists (Gospel writers) or of the Annunciation, displaying the Archangel Gabriel and the Virgin Mary. Since these are the gates through which the life-giving flesh and blood of God will enter the nave of the Church to be given to the people, it is fitting that the Virgin Mary is depicted on these gates (or similarly, it is fitting that sometimes the Gospel writers who brought us the message of God incarnate are depicted).
Directly above the Beautiful Gates (or Royal Doors), you may see an icon of the Mystical Supper (Last Supper), or perhaps Christ enthroned, and very likely a large cross.
The central doors are always flanked by an icon of Christ to the right, and the Virgin Mary and with the Christ child to the left. Next comes the patron saint or patronal feast of the parish—in Byzantine parishes, the patronal icon goes next to the Virgin Mary, but in Slavic parishes, the patronal icon is next to Christ. Often—though not always—St. John the Baptist is depicted to the right, either next to Christ or after the patron saint. Other well-loved saints, such as St. George or St. Nicholas, may be depicted on other panels.
Depending on the size of the iconostasis, you may see one or more rows of icons above the first tier of icons. These rows may depict the major feasts of the Church (based around Christ’s and the Virgin Mary’s lives), the twelve apostles (sometimes St. Matthias is replaced by St. Paul), and/or Old Testament patriarchs and prophets.
Though not part of the iconostasis, when looking at the iconostasis you may be struck by a large iconographic representation behind the altar. In Byzantine parishes, this is almost always an icon of the Virgin Mary and Christ, known as the Panagia (all-holy). She usually has her arms open wide, and Christ is making a blessing, or may have his arms open wide, too. These open arms symbolize that she is “wider than the heavens” having “contained the uncontainable one” in her womb—and some see the open arms as an invitation of love to the world.
Slavic parishes sometimes depict the Resurrection of Christ, the Mystical (Last) Supper, or Christ enthroned in heaven and surrounded by angels in this space instead.
In a very real sense, the iconostasis and curtain separate the nave from the sanctuary—the common area from the Holy of Holies. But unlike the Holy of Holies in the Old Testament temple, this Holy of Holies is accessible. We can see it, and in fact, the icons draw our eyes toward it. And at the apex of every Liturgy, God enters the Holy of Holies in his body and his blood, and then condescends to come to us through the Beautiful Gates. And finally, he gives himself to us.
This is the true faith that established the universe!
If they wanted to, Western Rite parishes could build an authentic English “Rood Screen,” a feature which developed quite independenty of the eastern iconostas but ended up very similar in form. Rood screens were often destroyed during the excesses of the Reformation, but there are still many surviving examples. See “Rood Screen” at Wikipedia.
A proper Orthodox description of the “Last Supper” icon is “Mystical Supper”. And the Mother of God in the apse of the sanctuary is known as the Platitera twn Ouranwn, or She Who is Wider Than the heavens (because she contained the uncontainable One) and that is why her arms are outstretched.
Thanks for the comments, John!