At first the Brothers of the Bridge just kept little inns at river crossings，wheretravelers might stop.But soon they built their own bridges at these places.Often the Brothers made the roadway over the bridge so narrow at the middle of the bridge that only one horseman could cross at a time.This was to make it hard for robbers and soldiers to dash across and attack travelers.Of course such bridges weren’t much good for wagons，but the roads weren’t much good for wagons，either.Many of these bridges were strongly fortified with huge stone towers at each end，so that they could stop robber bands or even armies from crossing.
Probably the most famous bridge of the Middle Ages was the old London Bridge overthe river Thames.It had houses built on it，NO.86-1A MEDIEVAL BRIDGE CA-
HORS，FRANCE
（法国卡奥尔一座中世纪的桥）
Courtesy of Pratt Institute
some of them four and five stories high，but its foundations weren’t very solid and so it was always needing repairs.Parts of it even fell down at various times.You remember “London Bridgeis Falling Down”？At that，it lasted，with many repairs，from 1209to 1831，when it was torn down to make way for the new London Bridge.
As you know，after the Middle Ages came the Renaissance，when many famous bridges were built.I’d like to tell you about some of them if I had more space—aboutthe most photographed bridge in the world，the Bridge of Sighs in Venice，and about the Ponte Vecchio in Florence，and about the oldest bridge in Paris，which is still called the Pont Neuf or the New Bridge，and about the Pont Royal and the Pont Marie，also in Paris.All these are stone bridge.
Modern bridge building began with the railroads，about 1830.At that time iron bridges were built.Then came steel bridges，and finally concrete and reinforced concrete bridges.Reinforced concrete bridges have iron bars inside the concrete to make them stronger.Many handsome reinforced concrete bridges have been built in recent years.Generally，they are arch bridges—sometimes with one arch and sometimes with many.In the United States they are the favorite road bridges.
No.86-2BROOKLYN BRIDGE OVER THE EAST RIVER，NEW YORK（纽约东河上的布鲁克林桥）
Photograph by Ewing Galloway
The iron and steel bridges are often truss bridges.In fact，truss bridges are altogether modern.
Some of the earliest bridges in Asia and South America were suspension bridges.These were hung from cables of rope or vine and were pretty shaky.Some of them are still in use.When you cross one you can’t help hoping you’ll get over alive.Really they are quitestrong in spite of being so shaky.But I’d hate to try to cross one on an elephant —or in an automobile.
Modern suspension bridges are hung from steel cables.Most of them are very large and cost millions of dollars to build.One of the most famous is the Brooklyn Bridge over the East River at New York.Bigger ones have been built since，but this grandfather of modern suspension bridges is still considered one of the finest to look at.It could carry whole herds of elephants in safety.It does in fact carry herds of street cars and automobiles.
When you go for a trip next time，keep your eyes open for bridges.Many of the finest bridges in the world are right here in the United States.Some travelers play games with bridges as they travel along.In this game a suspension bridge counts 20points，a cantilever bridge 15points，an arch bridge 10points，a truss bridge 5point and a simple beam bridge 2points.Sometimes when you go over a bridge you can’t see what kind of bridge it is.All you can see are the railing and the roadway.That would count only one point.Whoever sees the bridge first，gets the points.
Last of all，I’ll tell you this.All bridges aren’t beautiful，but there are probably fewer ugly bridges than anything else we build；and even ugly bridges generally have an interesting story，if you can find out what it is.One of the ugliest bridges is in Barnstable，England.It has many arches，each one a different size.The size was not planned by an architect，but was determined by the amount of money every citizen donated.
No.86-3SKY-SCRAPERS OF NEW YORK（纽约的摩天大厦）Photograph by Brown Brothers
【中文阅读】
“现在，谁愿意单手倒立，和我一起托起这座大桥？”
我小时候，最喜欢读的一首诗是“桥上的霍拉提乌斯”。断桥救城，罗马英雄和他的两伙伴阻挡了整个敌军的进攻！每当我爸朗读这一段故事时，我就特别兴奋！诗中有几段我已烂熟于心，毫不费劲就能背出来。
桥上的霍拉提乌斯；每个人都知道霍拉提乌斯的故事，但并不是许多人都知道那座桥的故事。
那可是罗马的第一座桥，“三勇士”手握亮剑，伫立桥头，嘲笑不断逼近的敌军。它也是罗马的唯一的一座桥。
这是一座木桥，用斧头就能砍断。可它对罗马来说太重要了，所以就由祭司负责看管。据说霍拉提乌斯和那座老桥在保住了罗马城之后，祭司们亲手造了一座新桥。你有没有听说过，教皇是被当做“祭司长”来看待的？而祭司长只是一个头衔。你能想到教皇的这个头衔起源于霍拉提乌斯和他护桥的故事吗？古罗马当时的祭司长名叫庞蒂菲克斯.马克瑟穆斯（Pontifex Maximus），英语的意思是“最伟大的造桥者”。人们这样称呼他，因为他是当年造桥的主要负责人。因此“庞蒂菲克斯”
（pontifex）或“庞蒂菲”（pontiff），就开始有了“祭司”（priest）的意思，这也是为什么“祭司长”或“造桥者”成了教皇的头衔。
而pontiff 中的pont 又出现在另一个奇怪的用法中。想象一下，如果霍拉提乌斯突然看到一架水上飞机从头顶飞过，螺旋桨轰轰作响，“浮筒”（pontoons）在太阳下闪闪发光，他会想到什么呢？浮筒曾是一种用来支撑桥的小船。横搭在小船上的桥叫做“浮桥”。而在水上托起水上飞机的浮筒就是这样得名的，因为它们看起来像是支撑浮桥的小船。
现在我最好还是介绍一下桥的种类。它们并没有想象的那么多。实际上只有五种桥，太好了，因为就五种也就便于了解，好让我们看到哪种都能认得。
五种桥如下：第一种最简单，叫独木桥。而最简单的独木桥就是在小溪上横担一根木头。第二种是拱桥。彩虹会造一座美丽的拱桥，只不过人不能从上面走过。中国有许多好看的拱桥。第三种是吊桥。对猴子来说，攀在两棵树之间野葡萄藤是一种再好不过的吊桥。第四种桥的名称有点难记。它叫做悬臂桥。拿块木板，搭座悬臂桥看看。握住木板的一端，将另一端刚好碰到桌边，但不要放在桌上。这样木板就成了悬臂桥。悬臂桥是一种只在一头固定的独木桥。有点像游泳池跳水用的跳板。通常情况下，悬臂从溪流的两岸伸出，在中间会合。第五种是桁架桥。桁架桥指桥梁靠坚固的框架将各个部分牢牢固定。框架既可以按在桥面上方，也可以按在桥下，有点像自行车的车架。悬臂桥通常需要桁架来支撑。桁架桥可以是木制的，也可以用钢铁作材料。
就这五种桥。怎么没有谈到浮桥呢？其实浮桥就是最简易的独木桥，只不过没把桥梁担在桥墩上而是搭在船上。
最早的桥当然是独木桥。伟大的波斯王薛西斯于公元前480年攻打希腊时，造了一座横跨达达尼尔海峡的浮桥。
奇怪的是，曾经建造过像帕台农神庙那样完美建筑的希腊人却不会造桥。他们旅行时喜欢乘船，不喜欢走路，所以就不怎么需要桥。而且希腊的河流都非常窄，没有桥也能过，尽管有时可能要湿脚过河。
这又将我们带回到了罗马。罗马人直到现代还能算作最伟大的造桥者。条条大路通罗马，罗马路上都有桥。不但在意大利，就是在西班牙、法国、英国和奥地利，漂亮的罗马式大桥帮助了行人到达目的地。
罗马人造的桥有许多在使用了两千年后至今还依然挺立。那些木桥当然早就不在了，大多数是石桥，那些石块紧紧地衔合在一起，基本上不需要用灰泥加固。