(1) Observatories, _i.e._, circles in the first place; next something to mark the sight-lines to the clock-star for night work, to the rising or setting of the warning stars, and to the places of sunrise and sunset at the chief festivals. This something, we have learned, might be another circle, a standing stone, a dolmen, a cove, or a holed stone. A study of the sight-lines shows us that these collimation marks, as we may call them, were of set purpose, generally placed some distance away from the circles, so far that they would require to be illuminated in some way for the night and dawn observations. When there was no wind, one or more hollows in a stone, whether a menhir or a quoit, might have held grease to feed a wick or a pine-wood torch. But in a wind some shelter would be necessary, and the light might have been used in a cromlech or allée couverte. Stones have been found with such cups, and débris of fires have been found in cromlechs. It must not be forgotten that here there was no oil as in the Semitic countries whence, as we have seen, the immigrants came; and it was not a question of a light on the sight-line alone. If wood were used, it must have been kept dry for use, and whether wood or animal fat were employed the most practical and convenient way of lighting up would have been to keep a fire ever burning in some sheltered place. (2) Dwellings, which would be cromlechs or many-chambered barrows, according to the number of astronomer-priests at the station. These dwellings would require to be protected against the invasions of the local fauna, very different from what it is now, and for this a small, and on that account easily blocked, entrance would be an essential. These dwellings would naturally suggest themselves as the shelter place for the ever-burning fire or the supply of dry wood. Tradition points with no uncertain sound to the former existence of life and light in these “hollow hills.” Mr. MacRitchie’s book[127] contains a mine of most valuable and interesting information on this subject. (3) A water supply for drinking and bathing, which might be a spring, river or lake, according to the locality. Given a supply of food we have now provided for the shelter and protection of the astronomer and the man.