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旁白：来听历史课讲座的一部分。

Narrator: Listen to part of a lecture in a History class.

教授：古代世界的大多数城市都是小的，通常局限于河岸。

Professor: So most cities of the ancient world tended to be small, often limited to the banks of a river.

这些古老的城市无法跨越像河流这样的自然屏障，

These old cities couldn't really cross natural barriers like rivers,

或者建立在离水源很远的地方。

or be located very far from water sources.

但另一方面，罗马城市的规模却大得多。

But Roman cities, on the other hand, grew much larger.

首先，罗马人拥有更先进的技术。

Well, for one thing, the Romans had more advanced technology.

让我们来看看哪些罗马的发展，让他们的城市得以扩张。

Let's look at a couple of Roman developments that allowed their cities to expand.

允许罗马城市发展的一个进步，是他们先进的建筑材料。

One development that allowed Roman cities to grow was their advanced building materials.

罗马人发明了一种特殊的混凝土，这种建筑材料会在水下变硬，

The Romans developed a special kind of concrete, a building material that would harden under water,

这种混凝土使建造新型结构成为可能。

and this concrete made new kinds of structures possible.

因为有特殊的混凝土，他们可以建造更好的桥梁，

because of the special concrete, they could build better bridges,

比如可以跨越广阔河流的桥梁，

bridges that could go across wide rivers,

比如那些大到可以用马车和马车运输设备和材料的桥梁。

bridges that were big enough to transport equipment and materials with wagons and carts.

罗马的城市可以在这条河的两岸发展，

Roman cities could grow on both sides of the river,

否则创造更大的城市是不可能的。

creating larger cities than would have been possible otherwise.

另一项帮助罗马城市扩张的发展是一种改良的运输新鲜、干净的水的方法。

Another development that helped Roman cities expand was an improved way to move fresh, clean water.

罗马人创造了一种特别有效的方式将其带给他们。

and the Romans created an especially effective way to bring it to them.

他们建造了一个叫做“渡槽”的建筑。

They built structures called "aqueducts".

现在，渡槽是一系列开放的通道，

Now, aqueducts are a series of open channels,

从山上的水源延伸到城市的水道。

waterways that stretch from water sources high in the mountains to cities.

它们经过了精心的规划和建造，高度稳定下降为城市提供了稳定的水流。

They were carefully planned and built so that a steady drop in altitude provided a steady flow of water to cities.

这些渡槽可以从很远的地方移动大量的水，

These aqueducts could move a tremendous amount of water over great distances,

甚至把淡水带到远离河流的地方。

and even bring fresh water to places far from rivers.

人们可以在没有靠近河流的情况下，有干净的饮用水和洗澡水。

people could have clean water for drinking and bathing without being located near a river.

因此，城市能够在新的地点变得更大。

So cities were able to grow larger in new locations.

<img src="/upload/ti/2427000-2428000/2427022/b002dded2e3c49aa9e1d16388d16f008.jpg">
<br>&nbsp;&nbsp;
<p>Using the examples from the lecture, explain two developments that allowed ancient Roman cities to expand.</p>