The chronology of the barrows is somewhat perplexing. There is hardly a single absolutely certain instance in which a socketed celt, a sword, or a socketed spear-head has been found in a barrow, associated with an interment;[752] and most antiquaries infer that the round barrows generally belong to the earliest period of the Bronze Age.[753] It would follow that during not less than four or five centuries the practice of raising mounds over graves was discontinued, and one could only wonder how it came to be revived at the beginning of the Iron Age. It has indeed been argued that the absence of swords is no proof that they were not used when barrows were being erected, but merely shows that it was not customary to bury costly weapons which were not habitually worn.[754] It seems difficult, however, to explain why a distinction should have been drawn between swords and socketed celts, on the one hand, and knives, daggers, and awls, which were often buried, on the other.[755] Some may accept the suggestion that in the later period of the Bronze Age, when cremation had presumably become general, the practice of burying weapons or ornaments had ceased;[756] but in the Early Iron Age it was not uncommon.[757] It would seem, moreover, that in one or two instances socketed weapons were laid with the dead;[758] and Dr. Arthur Evans, pointing out that an amber necklace, found in one of the barrows near Stonehenge, is identical in form and arrangement with the amber necklaces of Hallstatt, boldly affirms that the disk-shaped barrows of Wiltshire belong to the end of the Bronze Age.[759] Be this, however, as it may, it is morally certain that some of the glass beads which abounded in the graves of South Wiltshire were contemporary with socketed weapons; and a competent antiquary, who has diligently examined their associations, concludes that they belonged to the eighth and seventh centuries before the Christian era.[760] Moreover, an earthenware vessel of the kind which are called incense-cups, found in a barrow at Bulford, near Amesbury, was ornamented with concentric circles;[761] and, as we have seen,[762] this form of decoration, which is common on the covering stones of cists in Scotland and in the north of England,[763] is also characteristic of socketed celts and unknown on implements of earlier date. The number of celts which have been found in barrows is so small that it would be premature to lay stress upon the fact that only one belonged to the socketed type;[764] and there may have been some reason, of which we are ignorant, for the absence of spear-heads and swords. In Gaul, at all events, relics belonging to every phase of the bronze culture have been exhumed from burial mounds.[765]