It is necessary to anticipate here and to substantiate the contrast. The earliest written documents of Mesopotamia served a severely practical purpose; they facilitated the administration of large economic units, the temple communities. The earliest Egyptian inscriptions were legends on royal monuments or seal engravings identifying the king’s officials. The earliest representations in Mesopotamian art are preponderantly religious; in Egyptian art they celebrate royal achievements and consist of historical subjects. Monumental architecture consists, in Mesopotamia, of temples, in Egypt of royal tombs. The earliest civilized society of Mesopotamia crystallized in separate nuclei, a number of distinct, autonomous cities—clear-cut, self-assertive polities—with the surrounding lands to sustain each one. Egyptian society assumed the form of the single, united, but rural, domain of an absolute monarch. The evidence from Egypt, which is the more extensive, indicates the transition was neither slow nor gradual. It is true that towards the end of the prehistoric period certain innovations heralded the coming age. But when the change occurred it had the character of a crisis, affecting every aspect of life at once but passing within the space of a few generations. Then followed—from the middle of the First until the end of the Third Dynasty—a period of consolidation and experiment, and with this the formative phase of Egyptian civilization was concluded. Few things that mattered in Pharaonic Egypt were without roots in that first great age of creativity. In Mesopotamia a parallel development possessed a somewhat different character. It likewise affected every field of cultural activity at once, but it lacked the finality of its Egyptian counterpart. It cannot be said of Mesopotamia that its civilization evolved in all its significant aspects from the achievements of one short period, decisive as that had been. Mesopotamian history shows a succession of upheavals, at intervals of but a few centuries, which did more than modify its political complexion. For instance, the Sumerian language,[87] which was dominant throughout the formative phase of Mesopotamian civilization, was replaced by Semitic Akkadian during the second half of the third millennium. And the shift of the centre of power, in the third millennium, from Sumer in the extreme south to Babylonia in the centre, in the second millennium to Assyria, in the extreme north, brought with it important cultural changes. Yet notwithstanding all the changes, Mesopotamian civilization never lost its identity; its “form” was modified by its turbulent history, but it was never destroyed.