ARE you a good detective？Can you tell what part of the country a person comes from，just by hearing him talk？At least you can tell the difference between a Southerner and a New Englander by the sound of their voices and the way they pronounce their words.
Men of one part of a country talk differently from men of another part.Men from different countries are different in other ways.They wear different kinds of clothes，they have different kinds of laws they eat different kinds of food，they paint different kinds of pictures，they build different kinds of buildings.
When the Roman emperor Constantine became a Christian，the Christians in Rome came out of the catacombs and built basilicas for churches.But subject to the Roman emperor there were other Christians who lived a long way from Rome.The Roman Empire reached eastward into Asia.Many people in this eastern part of the empire were Christians，too.Under Constantine they began to build churches just as the Christians in Rome did.But，belonging to a different part of the world，the eastern Christians built their churches in their own way.They didn’t care much for basilicas.
The kind of buildings the eastern Christians built was called Byzantine.That is because Byzantium was the largest city in the eastern part of the Roman Empire.The city is still a large and important city，but you won’t find Byzantium on the map.Byzantium changed its name.Constantine went to live in Byzantium and made it his capital instead of Rome.When he did this he named the city Constantinople or City of Constantine.But you won’t find Constantinople on the modern map，either，for now it is called Istanbul.The old name，Byzantine，however，stuck to the architecture that began to be used there.
There was one very important difference between this Byzantine architecture and the basilican architecture.A Byzantine church always had some kind of dome on it.In some churches the dome was small；in some it was covered with a square roof so you could see the dome only from below，on the inside；in many churches there were several domes.
The Pantheon in Rome has a dome，but the Pantheon is not like the Byzantine style of building.The Pantheon’s dome is made of concrete.The domes of Byzantine churcheswere usually made of bricks or tiles.The Pantheon dome rests on a circular wall.The Byzantine domes cover a square space.
The plan of most Byzantine churches looks like this：.This kind of cross with all the arms equal is called a Greek cross.The central dome was generally right over the square in the center of the cross.
All these Byzantine buildings with domes were quite small until the Emperor Justinian came to rule.Justinian had his architects build the best and finest and biggest building ever built in the Byzantine style.We call it St.Sophia or Santa Sofia，but Sofia was not the name of any saint.Sofia means wisdom and the real name of Justinian’s church is Holy Wisdom.As most Americans call it St.Sophia，that is what we shall call it here.
See if you can understand how St.Sophia is built.In the middle is a huge dome.This dome rests on the top of four big arches that are shaped like croquet wickets.Each arch stands on one side of a square.
The bottom of the dome rests on top of each wicket or arch.
No.69-1INTERIOR OF ST.SOPHIA（圣索菲亚教堂内部）Courtesy of The University Prints
The spaces between the tops of the arches below the dome are not empty.They are filled in with brick so the bottom of the dome is resting on something all the way round.These spaces between the tops of the arches look like curved triangles pointed downward.The curved triangles are called pendentives.I hope you can remember that word pendentive.It is the use of pendentives that makes Byzantine architecture very different from other kinds.You won’t find any pendentives in the Pantheon in Rome，for instance.
In this picture you can see three of the arches under the dome and two of the pendentives between the arches.
As the dome of St.Sophia is made of bricks，the whole dome isn’t held together like a saucer or like the concrete Pantheon dome.This means that the dome pushes down on the walls that hold it up and also pushes outward or sideways on the walls.You know how a ladder leaning against the wall of a room will slide out at the bottom when a heavy man climbs the ladder unless the bottom is braced against something on the floor.Well，the dome pushes out in all directions just as the ladder does in one direction，and so there must be something to brace the walls to keep the dome from pushing them over.
The arches resting on the ground held the downward push of the dome.The architects of St.Sophia took care of the outward push very cleverly.On the outside of two of the arches，opposite each other，they built half-domes on walls reaching to the ground which braced the two arches just like book-ends pushing toward the middle of the building.They were props to hold the arches from falling outward.
Against the legs of the other two arches they built big piles of stone and brick and these piles kept the arches in place just like book-ends，too.These piles were called buttresses.
And then—after all this care and work—the dome of St.Sophia fell down！It collapsed a few years after it was finished.But we can’t blame the builders.An earthquake shook the bricks out of place and down came the dome.The builders couldn’t prevent an earthquake.
When they put the dome up again they made an improvement.All around the bottom of the new dome little windows were made—forty windows altogether.This let in such a band of light that the dome seems to be resting on light when you look up at it from inside，or as if it were hanging from the sky a few feet above the top of the four big arches.