Ge: Apsis, Abside; Fr: abside; Da: apsis, apside; Sw: absid; Fi: apsis
A whiff of Imperial power
The apse of a medieval church entails more than meets the eye. It is a decorative architectural detail, certainly. But during some 150 years in Northern Europe it was additionally used as a symbolic weapon in the local power struggle between Worldly Power (the King or ruler) and Spiritual Power (the Bishop or Pope).
Originally the apse was designed as an Imperial power symbol in pre-Christian Rome. It consisted of an outwardly protruding structure in the wall of an Imperial basilica. This was where the Emperor was seated on his throne during the elaborate rites of the Roman Emperor cult. The Christian Church transferred the apse's original power-related idea to its own ritual buildings, getting some free Imperial Glory in the bargain.
A protrusion emphasising the bishop’s power
Architecturally speaking, the apse is simple enough. It is a protrusion from the eastern (altar-side) wall (the chancel) of a medieval church. It is narrower than the chancel wall and has a lower roof. The geometry of the apse protrusion varies, from semicircular and polygonal to rectangular. Continental and Nordic churches have generally rounded or polygonal apses, while the medieval churches in Britain mostly have rectangular apses. In some churches, particularly in those of Byzantine origin, even multiple apses are found.
The apse, being right behind the altar, now housed the throne of the bishop, instead of the Emperor. Its ceiling was symbolic of Heaven and had a concave vault-like design. Decorative elements included "Majestas Domini", an iconographic stereotype that depicted "Christ as a Ruler" (as opposed to "Christ as the Saviour"). In the Majestas Domini stereotype Christ is shown sitting on a rainbow, a throne, or occasionally on a globe. He is surrounded by an almond-shaped Gloria, a "mandorla". The idea is not originally Christian, but was imported from Josiah 66, 1-4 ("Heaven is my throne and Earth my foot-stool") and Ezekiel 1, 26-28 (where there is talk of a powerful figure on a rainbow, surrounded by an almond-shaped light).
A spiritual disagreement
The point of it all -- both of the Imperial-looking apse and the Majestas Domini picture -- was to emphasise that Power emanated from Heaven, via its representatives on Earth (the Pope and the Bishop), not from secular rulers.
This was a particularly important to point make in Scandinavia, where Christianity had gained foothold relatively late (from ca 1000 AD onwards). The first people to convert to the new religion were understandably not ordinary people, but local kings and chiefs. They were the ones to build the first churches and consequently the ones to appoint and hire the priests.
Some time later, when the Papal Church hierarchy was trying to establish itself in the North, this state of affairs was no longer acceptable to the clerics. Priests should be appointed by Spiritual powers only, i.e. by the Bishop, the Pope’s local representative and hence, by extension, God’s representative.
Battling architecturally, to the last apse
How do apses fit into this clerical vs. secular argument? Well, an interesting matter is that in the North churches with apses were built only during a relatively brief period of 150 years, between approximately 1100 and 1250 AD. Before 1100 virtually all Scandinavian churches were built without apses. After 1250 the apses were again out of fashion.
This is also precisely the period when the Church organisation was still trying to get a firm grip on the region. Whenever a church was transferred from private to Church hands, it was immediately equipped with an apse, to show that from now on it belonged to the Bishop’s Spiritual domain -- that the Church hierarchy had won a victory. New churches belonging to the Papal Church hierarchy were also built with apses, to make the point of ownership and authority quite clear.
By 1250 AD, some 150 years later, the Papal Church had firmly established itself as an undisputed power in the Scandinavian religious sphere. Henceforth there was no need for architectural propaganda. No more apses were ever built to adorn medieval Scandinavian churches.
Of course, the stuggle itself -- between Wordly power and Spiritual power -- never really ceased, but from 1250 AD it was no longer fought by architectural means. One culmination of the continued struggle occured during the Reformation, when shrewd kings like Henry VIII (Eng) and Gustav Vasa (Swe) gained the upper hand. But the fight is still going on today, mainly in the Middle East, but also in parts of the Western world.
Wienberg, Jes: Enten – Eller. Apsidekirker i Norden, Hikuin 24, 1997