Three different kinds of ibis species are attested from ancient Egypt: the sacred ibis, the glossy ibis, and the northern bald ibis. Pictorial representations of the latter bird—easily recognizable by the shape of its body, the shorter legs, long curved beak, and the typical crest covering the back of the head—were used in writings of the noun akh and related words and notions (e.g., the blessed dead). We can deduce from modern observations that in ancient times this member of the ibis species used to dwell on rocky cliffs on the eastern bank of the Nile, that is, at the very place designated as the ideal rebirth and resurrection region (the akhet). Thus, the northern bald ibises might have been viewed as visitors and messengers from the other world—earthly manifestations of the blessed dead (the akhu). The material and pictorial evidence dealing with the northern bald ibis in ancient Egypt is accurate, precise, and elaborate in the early periods of Egyptian history (until the final phase of the third millennium BCE). Later, the representations of this bird became schematized and do not correspond to nature. Thus, they do not present us with any direct and convincing evidence for the presence of the northern bald ibis in Egypt, and, moreover, they most probably witness both the bird’s decline and its disappearance from the country.

The ba, whose notion spanned from the divine to the manifestation of the divine, and from the supernatural (or rather super-human) manifestation of the dead to the notion of the soul (psyche) or reputation, counts among the most important Egyptian religious concepts. The term and its hieroglyphic renderings are attested for all periods of ancient Egyptian history. In the process of time the word ba was written with various signs, including that of a stork (G 29), a ram (E 10), and a human-headed falcon (G 53). Its representation with sign G 29—the saddle-billed stork (Ephippiorhynchus senegalensis)—is both the earliest and the most attested depiction connected to the religious concept of the ba. Thus it serves as a crucial witness to the original meaning and main aspect of the ba.

The notion of akh, often translated as (effective) spirit, pointed toward many different meanings, such as the identity of the transfigured dead as well as that of living persons who acted efficaciously for (or on behalf of) their masters. The akh belonged to cardinal terms of ancient Egyptian religion and hence is often found in Egyptian religious texts, as well as in other textual and iconographic sources. Its basic meaning was related to effectiveness and reciprocal relationship that crossed the borderlines between different spheres.