When _menhirs_ are arranged in circles, either single or several together, they are called _cromlechs_. They are vast circuits of stones, generally arranged round a _dolmen_. The respect which was considered due to the dead appears to have converted these enclosures into places of pilgrimage, where, on certain days, public assemblies were held. These enclosures are sometimes circular, as in England, sometimes rectangular, as in Germany, and embrace one or more ranks. [Illustration: Fig. 143.--_Dolmen_ with a Circuit of Stones (_Cromlech_), in the Province of Constantine.] Fig. 143 represents a _dolmen_ with a circuit of stones, that is, a _cromlech_, which has been discovered in the province of Constantine; in fig. 144 we have a group of Danish _cromlechs_. [Illustration: Fig. 144.--Group of Danish _Cromlechs_.] Among all these various monuments the "passage-tombs" and the _tumuli_ are the only ones which will come within the scope of this work; for these only have furnished us with any relics of pre-historic times, and have given us any information with respect to the peoples who occupied a great part of Europe at a date far anterior to any traditionary record. These stone monuments, as we have already stated, are neither Celtic nor Druidical. The Celts--a nation which occupied a portion of Gaul at a period long before the Christian era--were altogether innocent of any megalithic construction. They found these monuments already in existence at the time of their immigration, and, doubtless, looked upon them with as much astonishment as is shown by observers of the present day. Whenever there appeared any advantage in utilising them, the Celts did not fail to avail themselves of them. The priests of this ancient people, the Druids, who plucked from off the oak the sacred mistletoe, performed their religious ceremonies in the depths of some obscure forest. Now, no _dolmen_ was ever built in the midst of a forest; all the stone monuments which now exist stand in comparatively unwooded parts of the country. We must, therefore, renounce the ancient and poetical idea which recognised in these _dolmens_ the sacrificial altars of the religion of our ancestors. Some _tumuli_ attain proportions which are really colossal. Among these is Silbury Hill, the largest in Great Britain, which is nearly 200 feet high. The enormous amount of labour which would be involved in constructions of this kind has led to the idea that they were not raised except in honour of chiefs and other great personages. On consulting those records of history which extend back to the most remote antiquity, we arrive at the fact that the custom of raising colossal tombs to the illustrious dead was one that was much in vogue in the ancient Eastern world. Traces of these monuments are found among the Hebrews, the Assyrians, the Greeks, the Egyptians, &c.