The earliest of the city states of the ancient Near East appeared at the southern end of the Mesopotamian plain, the area between the Tigris and Euphrates rivers in what is now Iraq. It was here that the civilization known as Sumer emerged in its earliest form in the fifth millennium. At first sight, the plain did not appear to be a likely home for a civilization. There were few natural resources, no timber, stone, or metals. Rainfall was limited, and what water there was rushed across the plain in the annual flood of melted snow. As the plain fell only 20 meters in 500 kilometers, the beds of the rivers shifted constantly. It was this that made the organization of irrigation, particularly the building of canals to channel and preserve the water, essential. Once this was done and the silt carried down by the rivers was planted, the rewards were rich: four to five times what rain-fed earth would produce. It was these conditions that allowed an elite to emerge, probably as an organizing class, and to sustain itself through the control of surplus crops.

It is difficult to isolate the factors that led to the next development—the emergence of urban settlements. The earliest, that of Eridu, about 4500 B.C.E., and Uruk, a thousand years later, center on impressive temple complexes built of mud brick. In some way, the elite had associated themselves with the power of the gods. Uruk, for instance, had two patron gods—Anu, the god of the sky and sovereign of all other gods, and Inanna, a goddess of love and war—and there were others, patrons of different cities. Human beings were at their mercy. The biblical story of the Flood may originate in Sumer. In the earliest version, the gods destroy the human race because its clamor had been so disturbing to them.

It used to be believed that before 3000 B.C.E. the political and economic life of the cities was centered on their temples, but it now seems probable that the cities had secular rulers from earliest times. Within the city lived administrators, craftspeople, and merchants. (Trading was important, as so many raw materials, the semiprecious stones for the decoration of the temples, timbers for roofs, and all metals, had to be imported.) An increasingly sophisticated system of administration led in about 3300 B.C.E. to the appearance of writing. The earliest script was based on logograms, with a symbol being used to express a whole word. The logograms were incised on damp clay tablets with a stylus with a wedge shape at its end. (The Romans called the shape cuneus and this gives the script its name of cuneiform.) Two thousand logograms have been recorded from these early centuries of writing. A more economical approach was to use a sign to express not a whole word but a single syllable. (To take an example: the Sumerian word for " head” was “sag.” Whenever a word including a syllable in which the sound “sag” was to be written, the sign for “sag" could be used to express that syllable with the remaining syllables of the word expressed by other signs.) By 2300 B.C.E. the number of signs required had been reduced to 600, and the range of words that could be expressed had widened. Texts dealing with economic matters predominated, as they always had done; but at this point works of theology, literature, history, and law also appeared.

Other innovations of the late fourth millennium include the wheel, probably developed first as a more efficient way of making pottery and then transferred to transport. A tablet engraved about 3000 B.C.E. provides the earliest known example from Sumer, a roofed boxlike sledge mounted on four solid wheels. A major development was the discovery, again about 3000 B.C.E., that if copper, which had been known in Mesopotamia since about 3500 B.C.E., was mixed with tin, a much harder metal, bronze, would result. Although copper and stone tools continued to be used, bronze was far more successful in creating sharp edges that could be used as anything from saws and scythes to weapons. The period from 3000 to 1000 B.C.E., when the use of bronze became widespread, is normally referred to as the Bronze Age.

古代西亚地区最早的城邦出现在美索不达米亚平原的最南边， 这个位于底格里斯河和幼发拉底河之间如今被称为伊拉克的地区。5 000 年前，正是在这里出现了苏美尔文明的早期形态。乍看之下，这个平原并不像是一个（古老）文明的发源地。这里自然资源稀缺，木材、石料以及金属都极其匮乏。降雨量有限，当地水资源的主要来源是每年冰雪 融化导致的冲过平原的洪水。因为该平原在方圆 500 公里内的海拔落差只有 20 米，所以河床（的位置）不断地发生变化。这就使得灌溉系统的规划至关重要，特别是（如何）建造水渠以疏导和保存水资源。 这些灌溉工程完成以及河流冲积下的淤泥就会沉积在此处，带来的回报相当可观：其产出量会比靠雨水滋润的土地高出 4~5 倍。正是这些环境条件使得在该地诞生了一个可能充当管理阶层的“精英” ，这一阶层通过对余粮的控制来养活自己。 很难把导致苏美尔文明进一步发展， 即城市聚居点的出现的诸多因素孤立起来看待。 其中最早的， 如公元前 4500 年的埃利都以及之后 1000 年出现的乌鲁克， 都以用泥砖建造的令人惊叹的庙宇群为中心。通过某些方式，这些“精英”将自己与神灵之力联系在一起。 以乌鲁克为例， 这个城邦有两个守护神——天神以及众神之主安努和爱与战争女神伊南娜——不同的城市还有其他的守护神。 人类受神灵庇佑且掌控。 圣经中关于洪水的故事可能起源于苏美尔。在最早的版本中，神灵们意图毁灭人类，因为人类太过喧嚣吵闹令诸神厌烦不已。 曾经，人们认为公元前 3000 年之前，这些城邦的政治经济生活是以庙宇群为中心的，但是现在看来，这些城邦很可能早期就有世俗的统治者。城邦中生活着管理者们、手工艺人以及商人。 （因为有如此多的原材料、装饰庙宇用的半宝石石料、建造屋顶用的木材以及所有的金属都必须进口，贸易就显得很重要了。 ）一个日益复杂的管理系统促使了书写在公元前 3300 年左右的诞生。最早的手写体以缩记符为基础，用符号来表达一个词。 这些字符是用楔形状的铁笔， 被雕刻在潮湿的陶土版上 （因此字符末端也呈楔形） 。（古罗马人把这种形状称之为楔形（cuneus）并把这种手写体称之为楔形文字（cuneiform） 。 ）这些早期的书写文字记录了 2000 个这样的字符。后来出现一种更加方便的书写方法：使用一个符号去代表一个音节而非整个单词。 （如，在苏美尔语中表示“头”的词是“sag” 。每当一个词中含有“sag”这个音节，书写时都会写上“sag” ，“sag”被用于表达这一发音，而该词其他部分的发音则会用其他的符号来表达。 ）到公元前 2300 年，书写所需用到的符号数量下降到了 600 个。单词表达的范围却扩大了。有关经济方面的文本占主导地位，它们历来如此；但同时，关于神学、文学、历史和法律的作品也孕育而生了。 4000 年前的晚期的发明还包括轮子，这一发明最初可能是用于提高陶器的生产效率的，而后被应用到交通运输上。雕刻于约公元前 3000 年、来自苏美尔的一块陶土板上提供了已知最早的例证： 一个带顶棚的箱状雪橇被安装在四个实心的轮子上。 一个重大进展同样也发生在约公元前 3000 年， 铜在约公元前 3500 年就为美索不达米亚人所熟知， 如果将铜和锡混合在一起， 就可以制造出一种更坚硬的金属——青铜。 虽然铜制和石器还在继续被使用，但是青铜器更受欢迎，因为它可以被铸成锋利的边缘应用到锯、镰刀和武器等各方面。 公元前 3000 年到公元前 1000 年青铜器被广泛使用的这一时期通常被称为青铜时代。