The Cathedral of Trier is the oldest Roman Catholic church in Germany, with a main chapel made of Roman brick arranged in five symmetrical sections and an exterior apsidal semi-cylinder. The Church of St. Peter is one of the oldest churches in the Christian world, carved into a mountainside with floor mosaics and frescoes on the right side of its altar and a stone altar and platform. The Etchmiadzin Cathedral is one of the oldest cathedrals worldwide, built following Armenia's adoption of Christianity in the 3rd century with wooden doors and Old Testament frescoes and a cruciform plan with central cupola and four apses.

2. The oldest Roman Catholic
Church in Trier, Germany,
the Cathedral of Trier is
known for its long life span.
The center of its main
chapel is made of Roman
brick and has five
symmetrical sections. It also
features an apsidal semi-
cylinder on its exterior
façade.

3. This Serbian Orthodox
Church is the oldest church in
Serbia. Founded during the
Roman rule, it serves as the
ecclesiastical seat of the
Serbian church. It features
massive columns and an
octagonal tower that
conceals an inner cupola.

4. The Santa Maria Church in
Trastevere is a minor basilica that
is one of the oldest churches in
the whole of Rome. It has a very
basic floor plan and wall structure
and presents 22 granite columns
with Corinthian and Ionic capitals.
Its interior is filled with mosaics by
Pietro Cavallini.

5. Known as the largest church in the
world, the St. Peter’s Basilica is also
the most popular Christian church
today. It is known as a place of
pilgrimage especially among
Catholics and is considered among
the holiest Catholic sites. This
church is also regarded as the
greatest building of its age in terms
of architecture.

6. Also known as The Church of 100
Doors, the Panagia Ektatontapiliani
is a historic church on the island of
Paros. It features a main chapel
that is surrounded by two chapels
and it literally has one hundred
doors.

7. The oldest basilica in Milan, the
Basilica of Sant’Amborgio has a
hut-shaped façade which features
two orders of loggias. Its lower
loggia has three arcades while its
upper loggia used to be where the
bishops blessed the citizens. The
arcades are supported by pillars
and are flanked by semi-columns.

8. Considered one of the oldest
churches of the Christian world,
the Church of St. Peter features a
cave carved into the
mountainside of Mount Starius. It
has floor mosaics and frescoes
on the right side of its altar. It
has a stone altar at its middle
with a stonework platform on its
top.

9. The main cathedral of the Armenian
Apostolic Church, the Etchmiadzin
Cathedral is one of the oldest
cathedrals in the world. It was built
following the adoption of Armenia
of Christianity during the third
century. It has wooden doors and
frescoes of scenes from the Old
Testament. It also has a cruciform
plan with a central cupola, piers,
and four apses.

10. One of the oldest church buildings
in the Holy Land, this church is now
an archeological site. It was built
during the time when Christians
were persecuted by the Roman
Empire. Among the most notable
features of this church is its large
mosaic that contains a Greek
inscription and several geometric
figures and Christian symbols.

11. Known as the earliest identified
Christian house church in Syria,
this church was converted into a
house of worship following the
conquest of the Persians. It
features a house with a separate
hall-like room as well as frescoes
that serve as its baptistery. Its
interior is also filled with ancient
Christian paintings.