Tomb of a persecutor

The Cathedral of Saint Domnius is the Catholic cathedral in Split, Croatia. It is regarded as the oldest Catholic cathedral in the world that remains in use in its original structure. Built as the Mausoleum of Diocletian in 305, it is the second oldest structure used by any Christian cathedral.

Temple, church, mosque

The Arch of Galerius and the Rotunda are neighboring early 4th-century monuments in the city of Thessaloniki, in the region of Central Macedonia in northern Greece.The Roman Emperor Galerius commissioned these two structures as elements of an imperial precinct linked to his Thessaloniki palace. The Emperor Theodosius ordered its conversion into a Christian church in the late 4th century. Some of the original mosaics have survived -- for example, a band depicting saints with hands raised in prayer.

The building was used as a church for over 1,200 years until the city fell to the Ottomans. In 1590 it was converted into a mosque, called the Mosque of Suleyman Hortaji Effendi, and a minaret was added to the structure. It was used as a mosque until 1912, when the Greeks captured the city during the Balkan War. Greek Orthodox officials reconsecrated the structure as a church, and they left the minaret.

Basilica of SS. Cosmas and Damian

The Basilica of SS. Cosmas and Damian is a church in the Roman Forum, parts of which incorporate original Roman buildings. The circular building at the entrance onto the Forum (not used today) was built in the early 4th century as a Roman temple. The main building was perhaps the library of an imperial forum. It became a church in 527 and contains important but much-restored early Christian art, especially in its mosaics. Today it is one of the ancient churches called tituli, of which cardinals are patrons as cardinal-deacons.

The pope's cathedral

The Cathedral of the Most Holy Savior and of Saints John the Baptist and the Evangelist in the Lateran is the cathedral church of the Diocese of Rome and serves as the seat of the Bishop of Rome, i.e., the pope. It is the oldest and highest ranking of the four papal major basilicas, giving it the unique title of "archbasilica." Because it is the oldest public church in the city of Rome, it is the oldest and most important basilica of the Western world. It was consecrated in 324.

Greek island church

Panagia Ekatontapiliani (literally the church with 1,000 doors) or Panagia Katapoliani is a historic Byzantine church complex in Parikia town, on the island of Paros in Greece. The church complex contains a main chapel surrounded by two more chapels and a baptistery with a cruciform font.

The church dates to 326. Its oldest features likely predate the adoption of Christianity as the state religion of the Roman Empire in 391. The church was purportedly founded by the mother of the Roman Emperor Constantine the Great (ruled 306–337), St. Helena, during her pilgrimage to the Holy Land when she stopped to worship at a chapel on the island.

Stavrovouni Monastery

Stavrovouni Monastery is a Greek Orthodox monastery that stands on the top of a hill called Stavrovouni in Cyprus. It was founded by St. Helena (Constantine's mother) in around 327–329 and is one of many places where one can see a piece of the Holy Cross.

Christendom's best-known church

The best-known church in Christendom is one of its oldest—St. Peter's Basilica in Rome. It is also the largest church in the world and is built on the burial site of St. Peter the Apostle. Construction of the present basilica, which replaced Old St. Peter's Basilica from the 4th century, began in 1506.

St. George in Sofia

The Church of St. George is an Early Christian red brick rotunda that is considered the oldest building in Sofia, the capital of Bulgaria. Built by the Romans in the 4th century, it is famous for the frescoes inside the central dome. Painted over during the Ottoman period, when the building was used as a mosque, these frescoes were only uncovered and restored in the 20th century.

Santa Maria in Trastevere

The basic floor plan and wall structure of the Basilica of Santa Maria in Trastevere in Rome date to the 340s, and much of the structure to 1140-43. The first sanctuary was built in 221 and 227 by Pope Callixtus I and later completed by Pope Julius I. The church has large areas of important mosaics from the late 13th century by Pietro Cavallini.

St. Peter in Trier

The Cathedral of St. Peter in Trier is a Catholic church in Germany's Rhineland-Palatinate. It is the oldest church in Germany. The central part of the nave was built of Roman brick in the early 4th century, resulting in a cathedral that was added onto gradually in different eras. In 1986 the church was listed as a UNESCO World Heritage Site, as part of the Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier.

Lullingstane Chapel

Lullingstone Roman Villa was built during the Roman occupation of Britain, situated near the village of Eynsford in Kent, England. Constructed in the 1st century, perhaps around A.D. 80-90, the house was repeatedly expanded and occupied until it was destroyed by fire in the 5th century. The occupants were wealthy Romans or native Britons who had adopted Roman customs.

Some evidence found on site suggests that about A. D. 150, the villa was considerably enlarged and may have been used as the country retreat of the governors of the Roman province of Britannia. Two sculpted marble busts found in the cellar may be those of Pertinax, governor in 185-186, and his father-in-law, Publius Helvius Successus. In the 4th century, a room, probably already in religious use, was converted to a Christian chapel or house church, the earliest known in the British Isles.

In the Anglo-Saxon period, the ruins of a Roman temple-mausoleum on the site of the villa were incorporated into a Christian chapel (Lullingstane Chapel) that was extant at the time of the Norman Conquest, one of the earliest known chapels in the country.

Hagia Irene, Istanbul

Hagia Irene, or "Holy Peace," is a Greek Orthodox church located in Istanbul, Turkey. Built in the 6th century, it is one of the few churches in Istanbul that has not been converted into a mosque. The Hagia Irene today operates as a museum and, because of its fine acoustics, a concert hall. Here it is shown in front of the more famous Hagia Sophia, which was built later.