Right up to and into the present century the inhabitants of Linköping lived close together in buildings which accommodated not only dwellings but also cowhouses, pigsties and stables. Both human beings and animals produced waste which was often placed straight on to the ground in the yard. This caused the pollution both of the few wells and of the river. Since the town is on a slope which goes clown to the river, the contamination of the river water must have been considerable. That people lived so close together is an important explanatory factor regarding the fact that mortality, to the extent that we know anything about it, was for a long time so much higher in the towns than in the countryside. Especially infan t mortali ty ( the rate of death during the first year of life) was periodically extremely high, sometimes close on 50%. In this respect there was little difference between the small Swedish towns and the larger towns in other European countries. Despi te the fact that Linköping was for a long time a small town it was a dangerous place to live - so dangerous, indeed, that there were periods when a considerable inflow of people was needed in order for the population leve! to be maintained. Of decisive importance when it came to health in the town was how water-supply, sewage and hygiene were dealt with. The river Stångån had the central role wi th regard to all three. The essay also takes up a number of other questions of importance for health and hygiene. Today the river is still the source of the water supply of many of the inhabitants of Linköping, and in recent years the quality of its water has been very considerably improved. Now there is discussion as to how angling can best be arranged - and bathing is possible too. There has been an increase in environmental awareness, and the town's watersupplier has pointed out that water is not so self-evident as right as the air we breathe. There is also talk of establishing extensive wetlands at the mouth of the river in order to rid the sewage of nitrogen and thereby counteract the eutrophication of the lake Roxen. But probably we shall have to live with more nutrientrich waterways than before, even though the rate of increase has levelled off. At the same time as there have been improvements, however, there has been an increase in vulnerability. History offers many examples of what happens in modern towns in times of war and crisis - take, for instance, the crises in recent years in connection with the distintegration of Eastern Europe. Diseases which usually occur only in Third World countries can quickly become epidemic in industrialised countries if the water and sewage systems are knocked out. Our old knowledge of how to handle water and foodstuffs in primitive conditions is on its way to disappearing in modern society. Other threats to our future environment are connected with new synthetic substances which are added to our waterways - substances we do not today know the eff ects of. There is also the deluge of heavy metals. Thus our epoch, like every other, has questions of survival to deal with, but the fact remains: never before have so many been so healthy as now.