The fourth collection, the Atharva-veda, attained to this position only after a long struggle. Judged both by its language and by that portion of its matter which is analogous to the contents of the Rigveda, the Atharva-veda came into existence considerably later than that Veda. In form it is similar to the Rigveda, consisting for the most part of metrical hymns, many of which are taken from the last book of the older collection. In spirit, however, it is not only entirely different from the Rigveda, but represents a much more primitive stage of thought. While the Rigveda deals almost exclusively with the higher gods as conceived by a comparatively advanced and refined sacerdotal class, the Atharva-veda is, in the main, a book of spells and incantations appealing to the demon world, and teems with notions about witchcraft current among the lower grades of the population, and derived from an immemorial antiquity. These two, thus complementary to each other in contents, are obviously the most important of the four Vedas. As representing religious ideas at an earlier stage than any other literary monuments of the ancient world, they are of inestimable value to those who study the evolution of religious beliefs. The creative period of the Vedas at length came to an end. It was followed by an epoch in which there no longer seemed any need to offer up new prayers to the gods, but it appeared more meritorious to repeat those made by the holy seers of bygone generations, and handed down from father to son in various priestly families. The old hymns thus came to be successively gathered together in the Vedic collections already mentioned and in this form acquired an ever-increasing sanctity. Having ceased to produce poetry, the priesthood transferred their creative energies to the elaboration of the sacrificial ceremonial. The result was a ritual system far surpassing in complexity of detail anything the world has elsewhere known. The main importance of the old Vedic hymns and formulas now came to be their application to the innumerable details of the sacrifice. Around this combination of sacred verse and rite a new body of doctrine grew up in sacerdotal tradition, and finally assumed definite shape in the guise of distinct theological treatises entitled Brahmanas, "books dealing with devotion or prayer" (brahman). They evidently did not come into being till a time when the hymns were already deemed ancient and sacred revelations, the priestly custodians of which no longer fully understood their meaning owing to the change undergone by the language. They are written in prose throughout, and are in some cases accented, like the Vedas themselves. They are thus notable as representing the oldest prose writing of the Indo-European family. Their style is, indeed, cumbrous, rambling, and disjointed, but distinct progress towards greater facility is observable within this literary period.