the wedding-hymn of the union of Soma (no doubt the moon) and the dawn would be wholly unusual.
The constant grouping of gods in the Ṛgveda comes to formal expression in the practice of joint invocation, which finds its natural starting-point in the concept of heaven and earth, who are far oftener worshipped as joint than as separate deities. Even Mitra and Varuṇa are much more frequently a pair than taken individually, and this use may be old, since Ahura and Mithra are thus coupled in the Avesta. A more curious compound is Indra and Varuṇa, the warlike god and the slayer of Vṛtra united with the divinity who supports men in peace and wisdom. Indra is much more often conjoined with Agni, and the pair show in the main the characteristics of the former god, though something of Agni's priestly nature is also ascribed to them. With Viṣṇu Indra strides out boldly, with Vāyu he drinks the soma, with Pūṣan he slays Vṛtras, and to their joint abode the goat conveys the sacrificial horse after death. Soma is invoked with Pusan and with Rudra, Agni very rarely with Soma and Parjanya. A more natural pair are Parjanya and Vāta ("Rain" and "Wind"), and similar unions are Day and Night, and Sun and Moon. Naturally enough, these dualities develop little distinct character.
Of groups of gods the most important are the Maruts, who are numbered now as twenty-one and now as a hundred and eighty and who are Indra's followers, although as Rudras they are occasionally associated with Rudra as their father. The Ādityas are smaller in number, being given as seven or eight, while the Vasus are indeterminate in number as in character, the name denoting no more than "the Bright Ones." All the deities are summed up in the concept Viśve Devāḥ ("All-Gods"), but though originally intended to include all, the term even in the Ṛgveda becomes applied to a special body who are named together with other groups, such as the Vasus and the Ādityas.
An odd and curious group of deities is that of the Sādhyas,
