It is possible to create borders as it is possible to write constitutions or to alter a legal system. But after having been created, constitutions or legal systems begin to live in an autonomous way. They become adjusted to and redefined by the complex social conditions into which they are embedded and, in turn, they reshape them. The same is true with state borders. They are a crucial factor in forming their respective societies and they have a meaning which reflects the society they are embedded in.

Therefore, although borders may be artificially drawn, they become socio-historical phenomena of their own. If they are abolished, as they sometimes are, they leave traces which hardly ever disappear. The border between East and West Germany, for example, which existed for only 45 years continues to exist in social and cultural terms and will do so for a long time to come. This does not mean that Germany will necessarily break up again. But it will continue to be internally marked by a difference. This difference will certainly change its meaning, but it will live on as such. Likewise, many borders which have disappeared since long, still can be made visible as differences in mentalities, popular culture, dialect or voting behavior.

If societies are shaped by borders and if borders leave long-lasting traces research on present and past borders could be one of the most important topics of historical and social research in general, though certainly not the only one.

But there is an additional complication. The concept of border itself can have and has had different meanings in different times and places. And these meanings are sometimes inadvertently confounded. The ensuing confusion itself is usually used in a meaningful way.

To give one example: natural borders. In history, high mountains, extended marshes, or thick woodlands have kept cultures and languages in separation. They have enabled quite diverse and small cultures to survive as can be seen in the Caucasus mountains or even in the much smaller Alps. By contrast, it took some time until rivers which are certainly a natural phenomenon came to be considered as natural borders. They were easily crossed, used as a means for transportation or for irrigation. Therefore, cultures used to thrive along rivers: the Indus, the Ganga, the Yang-tse, the Huang-ho, the Nile, the Euphrates, the Volga etc. Even the Rhine was not a border until modern times. It would have been suicidal for the Roman Empire if it would have chosen the Rhine as a border to fence of the barbaric tribes of the East. The Romans erected their border, the Limes, east of the Rhine inland and for some time they were successful in keeping off the wilderness.

Just to illustrate my first observation: The Roman Empire has vanished for a long time. The German population has forgotten the Limes centuries ago, if they did not learn about it in modern schools. But the social and cultural traces of the limes are still to be felt in differences between those regions of Germany which had once been under Roman rule and those who had not.

If rivers became quasi natural borders this has to do with the genesis of the modern state and – at the same time – with progress in cartography. The modern state tended to homogenize its inhabitants, differentiating between citizens and non-citizens, between ethnic majorities and minorities. Likewise it tended to homogenize its territory in a legal sense. Rivers were now especially convenient in tracing borders since they – and their thalweg – could be thought of as sharply drawn lines.

The idea that each state has or should have one sovereign people, that this people was defined by one culture and one language was rather successfully realized in France and Britain. Linguistic homogenization was very successful there leaving only small minorities with little social and cultural prestige. In Central and Eastern Europe the situation was different. The multicultural empires knew ethnic and cultural hierarchies but in a strict sense they hardly strove for cultural and linguistic homogenization; and when they did they tended to fall apart. The national states which were carved out of the dying empires inherited some of the cultural diversity of these empires. But they had hardly any political means to cope with it. In some cases they were able to institutionalize some tolerance. In most cases minorities were defined and treated as a "problem" – ultimately to be solved by assimilation, relocation or worse.

Usually, attempts to assimilate culturally diverse parts of the population resulted in resistance and - at least - in internal strains which were difficult to solve. These effects could be reinforced under the threat of territorial secession. Therefore, modern national states were internally unstable if they were composed of culturally divergent populations, and the attempt to increase homogeneity in order to thwart destabilizing tendencies could result in increasing instability.

Thus, the state borders had not only the function to contribute to defining a national identity. They were instrumental in creating internal conflicts. In this way, modern borders had a deeply contradictory meaning which was translated into different kinds of strains. But their function went even further, and they had unintended but crucial consequences.

If you look at borders you somehow know there is a different world beyond. In other terms, borders create the difference between here and there which is necessarily thought to be essential. This difference is at the same time uncanny and fascinating. On the one hand it helps to create a collective identity, and on the other hand it threatens this very identity.

There are two possible ways to react to this uneasy difference. The first one is simply to turn the back to the border. The outside world simply does not exist in any real sense. This reaction seems to be rather typical. In Berlin before 1989 the wall was often ignored by many people in East and West. They did not even think about the other side although they knew that something was there. The Wall, the demarcation of a difference, was not looked at and remained unconscious. Indeed this attitude towards borders is fairly common and one of the factors which help to inscribe borders into society. Along recently drawn borders this attitude helps to gradually wipe out collective memory. Certainly, some traces of history continue to exist and to influence behavior. But the population concerned cannot read them any more. They are visible only to the informed outsider.

This kind of behavior is reflected even by a certain kind of map-making in which one country is represented like an island, surrounded by only one color: the outside world. Bohemia was finally located at the sea. This type of maps was particularly common in the socialist states which were particularly prone to deny historical contexts and to foster the rewriting of complex regional or cultural histories into simple national tales.

On the other hand, the fascination created by borders, by the difference of the other side, can produce a quite opposite type of behavior as well. It is then an invitation to cross it legally or illegally and to experience the thrill of the difference. There may be thought different types of border-crossers. For example, explorers who look for adventurous experiences or who simply want to extend their knowledge into new and fascinating territories. They may expose their courage and their experience later at home, gaining social recognition and acquiring some of the fascination qualities ascribed to the strange country.

This type of border-crossing helps to render collective identities more conscious and in this way to reaffirm them on the one hand and put them into danger on the other hand. In fact there are analogous phenomena of social perception as well. Sexual border crossing, e.g., reaffirms and undermines traditional gender roles at the same time. And it is easily perceived as a threat to normal identity. The same feelings can be seen in face of the crossing of the borders of scholarly disciplines. Orderly cooperation which may be compared to the tourism of official delegations and which is equally sterile can be contrasted by maverick scientists who ignore borders and threaten regular scholarship and the disciplinary identity it normally bestows on its meek inhabitants.

Another possible border-crosser who is attracted to the other side by quite different motives, are the professional smugglers. They act illegally, transporting products clandestinely from one side to the other. But persons smuggling pictures, poems, ideas or feelings from one side to the other tend to be seen as dangerous. Since their motives are not necessarily very honorable they can be thought of as importing dangerous germs, bacteria and other infectious phenomena into a territory which normal people always strove to clean culturally, religiously and intellectually in order to produce an uncontaminated identity.

It is possible to find other types of border-crossers and to differentiate them into subtypes. But it becomes clear, that their role is ambivalent and contradictory. On the one hand they provoke the reinforcement of institutions which watch upon the existence and effectiveness of the borders. Since border-crossers tend to circumvent or undermine any mechanisms invented by the border-guards these have to continuously refine their methods. In this way borders tend to become more and more difficult to cross. They force the crossers to be continuously inventive.

But the border crossers are themselves interested in the existence of borders. The smuggler would lose his livelihood without the borders he clandestinely strives to cross. The fascinated border-crosser would lose the thrill of his life if the other side was not fenced off and thus not very different. This might be one of the reasons why the unification of Europe might be an economically and politically sane enterprise and nevertheless be culturally boring.

The metaphorical pervasiveness of the concept of border can show that it has an essentially social content. Social classes and social milieus, subcultures as well as countries can be described or even tend to be described in spatial terms. This opens the way to readjust the perspective on borders as social phenomena. The spatial connotation of social and cultural "borders", the cultural and social connotations of state borders makes plausible the use of the concept as a "social form" as defined by the German sociologist Georg Simmel. It can show that the creation of borders may bring terrible hardships which need not to be elaborated here. But on the other hand borders can be seen as a condition for interest, for curiosity or for cognitive and emotional pleasure. The erotic connotations can be translated into other social and cultural realms. In this way, borders can not only be seen as ambivalent or maybe even positive stimuli, research on them can be helped by the use of those chains of metaphors which the concept of border seems to engender.