Christianity and the Greek alphabet
The situation was altered with the conversion of Egypt to Christianity in the 2nd and 3rd centuries ce. The new religion fought against the Egyptian polytheism and traditions, and with its victory the Greek script triumphed. From the beginning, Egyptian Christians used the Greek alphabet for writing their spoken Egyptian language. This practice involved enlarging the Greek alphabet with seven supplementary letters for Egyptian sounds not present in Greek. As a consequence, the knowledge of hieroglyphic writing quickly declined. The last datable evidence of the writing system is a graffito from the island of Philae, from August 24, 394, during the reign of the emperor Theodosius I. The language, as well as the writing system, of the Egyptian Christians is called Coptic.
Characteristics of hieroglyphic writing
The hieroglyphic writing system consists almost entirely of signs that represent recognizable objects in the natural or constructed world, and these can be grouped into three categories. The first is the logogram, in which a word is written (and read) by means of a single sign, providing both sound and meaning in itself. Ideograms can be read as the object they represent, such as 
, “wood, stick,” or can have extended meanings, such as the sun disk, ☉, which can be understood as “sun or (the solar god) Re” (in its phonetic reading “day” (read as H + r + w).
The second category is the phonogram, which represents a sound (or series of sounds) in the language. This group includes not only simple phonemes, which usually derive from logograms of the objects they depict but which acquired purely phonetic character, but also a much larger corpus of biliteral and triliteral signs (that is, signs that denote two or three sounds). Biliterals and triliterals, as well as logograms themselves, are often accompanied by the simple phonetic signs as a reading aid.
The third category of signs consists of determinatives, which carry no phonetic significance but are employed to specify meaning and assist in word division. For example, the phonetic writing p + r + t can signify the infinitive of the verb “to go,” the name of the winter season, or the word for “fruit, seed.” The meaning of the word is signaled by a terminal determinative that also acts as a word marker: the walking legs (
), the sun disk (☉), or the pellet sign (°), respectively. Generic determinatives are those that are denoting walking, running, or movement; the man with a hand to his mouth signifies words for eating, drinking, feeling, and perception; and the book roll is used for nouns pertaining to books, writing, and abstract concepts.
Egyptian inscriptions usually employed a combination of all three categories of signs, with liberal allowance for variation in spelling and in the grouping of signs. Egyptian generally avoided the writing of vowels aside from the semivowels i, y, and w; thus, the hieroglyphic system represents for the most part only the consonants of words. Pronunciation of Egyptian, therefore, is imperfectly reflected in the hieroglyphic writing system.
Number of symbols
In the classical period of Egyptian writing, the number of hieroglyphs totaled approximately 700. Their number multiplied considerably in the late period (which began about 600 bce); this proliferation occurred because scholars began to invent new forms or signs. The additional hieroglyphs were, however, always in accordance with the principles that had governed Egyptian writing from its beginnings. The hieroglyphic system remained flexible throughout all periods, always open to innovation, even though, as with every writing system, convention played a preponderant role.
Direction of writing
Hieroglyphic inscriptions were preferentially written from right to left, with the direction of reading indicated by the orientation of the signs, which normally face toward the beginning of the text. The right-to-left orientation in writing was scrupulously observed in the cursive form of the script, called hieratic (see below). Reversals of orientation in the writing of individual signs are relatively rare and were incorporated for either religious or decorative purposes.
Because Egyptian monuments were decorated according to strict conventions of symmetry, temples and tombs are usually adorned with hieroglyphic texts that face in both directions, to provide a visual sense of axial balance. Inscriptions could be written either in horizontal rows or in vertical columns, a feature that was ideally suited for the decoration of monumental walls, doorways, and lintels. In two-dimensional scenes containing human or divine figures, hieroglyphic texts are closely associated with the figures to which they pertain. That is, the identifying name, epithet, and utterance of an individual are oriented in the same direction in which the figure itself faces. And as one might expect for a distinctly pictorial script, the preferential right-to-left orientation of the Egyptian writing system had an effect on the development of three-dimensional art as well. For example, the striding male stance used for statuary requires that the left foot be placed forward, a visual pose that derives from the prescribed stance of the human hieroglyphic figure in preferred right-oriented inscriptions.