Catacombs
2 of the 7 encyclopedias on this shelf carry an entry for Catacombs. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
caves or subterranean places for the burial of the dead, the bodies being placed in graves or recesses hollowed out in the sides of the cave. Caves of this kind were common among the Phoenicians, Greeks, Persians, and many Oriental nations. In Sicily and Asia Minor numerous excavations have been discovered containing sepulchers, and the catacombs near Naples are remarkably extensive. Those of Rome, however, are the most important. The term catacumbæ is said to have been originally applied to the district near Rome which contains the chapel of St. Sebastian, in the vaults of which, according to tradition, the body of St. Peter was first deposited; but (besides its general application) it is now applied in a special way to all the extensive subterranean burial-places in the neighborhood of Rome, which extend underneath the town itself as well as the neighboring country, and are said to contain not less than 6,000,000 tombs. They consist of long, narrow galleries usually about 8 feet high and 5 feet wide, which branch off in all directions, forming a perfect maze of corridors. Different stories of galleries lie one below the other. Vertical shafts run up to the outer air, thus introducing light and air, though in small quantity. The graves or loculi lie longwise in the galleries. They are closed laterally by a slab. The earliest that can be dated with any certainty belongs to the year 111 A. D. In early times rich Christians constructed underground burying-places for themselves and their brethren, which they held as private property under the protection of the law. But in course of time, partly by their coming under the control of the Church and partly by accidents of proprietorship, these private burying-grounds were connected with each other, and became the property, not of particular individuals, but of the Christian community. In the 3d century A. D. there were already several such common burying-places belonging to the Christian congregations, and their number went on increasing till the time of Constantine, when the catacombs ceased to be used as burying-places. From the time of Constantine down to the 8th century they were used only as places of devotion and worship. During the siege of Rome by the Lombards in the 8th century the catacombs were in part destroyed, and soon became entirely inaccessible, so that they were forgotten, and only the careful and laborious in vestigations of moderns, among whom De Rossi (Roma Sotterranea) and Parker (The Catacombs) may be mentioned, have thrown anything like a complete light on the origin and history of the catacombs. There are extensive catacombs at Paris, consisting of old quarries from which has been obtained much of the material for the building of the city. In them are accumulated bones removed from cemeteries now built over.
Aiton's Encyclopedia (1910)
kat'a-koms, subterranean burial vaults. The custom of depositing the dead in cavern-like passages excavated in rock appears to be widespread. Catacombs have been found in Phoenicia, Asia Minor , on the coasts of Africa and Cyprus and Syria, Persia, Upper Egypt, Sicily, and elsewhere. Even the Aztecs of Central America deposited bodies, perhaps to the extent of millions, in rocky caverns which they enlarged and extended for the purpose. Abraham, it may be remembered, bargained with the children of Heth for the cave of Macpelah in which to bury his dead. The most extensive catacombs known are those excavated by the early Christians in the tufa or volcanic rock underlying the Campagna, or plain, near the city of Rome. The Romans cremated, but the Christians adopted the Jewish mode of burial. These catacombs were made by the early Christians as a place of burial, but came also to be used for refuge. Chapels and places for holding public worship were excavated in connection with them. The total length of the passages is from 350 to 900 miles. It is thought that they contain the bones of over 6,000,000 people. Many chambers, or vaults, are arranged along the sides of the passages. Those of important families appear to have been marked with slabs of stone bearing suitable inscriptions. Extensive catacombs are also found near Naples, and underground at Cairo. In excavating the stone of which the principal buildings of Paris are constructed the quarrymen extended their works to great distances beneath the surface of the city, leaving pillars to uphold the roof. When it became desirable to use the church cemeteries within the city for other purposes, the bones were collected and deposited in these old quarries, and they became places of burial. It is said that the catacombs of Paris contain several times as many people as now dwell within the city. Visitors accompany the officials on their periodical visits of inspection. The air of the catacombs is pure and dry. They are guarded carefully by the police to prevent their becoming the haunts of criminals. Guides carrying wax tapers conduct the party downward to a distance of seventy feet. There are many objects of special interest, including an underground chapel, memorial tablets, and a museum of curiosities. Some of the passages are hung with ghastly festoons of skulls and thigh bones. However desirous the visitor may be to visit these silent realms of death, he is thankful to reach the outer world again.