How were khutbahs given before invention of microphone?

How exactly did the Imam read the Qirat or deliver a Khutbah in the past before the invention of the microphone so as to make a group of 1000 - 2000 people hear him? In some case the population would reach 10000 as was the case of hajj in the past. How exactly was it it possible for such a huge population to pray behind one imam and still be able to hear his Qirat or his Khutbah?