In the ancient Near East, not many people could read. As a result, most information had to be shared with people by someone known as a herald. A herald was a man who could read and was given the task of going to all the different towns and cities where he would stand in the central meeting place of the town/city and in a loud voice read/shout a message to the people. In this way, people would hear the message that Cyrus wanted to proclaim.1
1 In the first year of Cyrus king of Persia, that the word of the LORD by the mouth of Jeremiah might be fulfilled, the LORD stirred up the spirit of Cyrus king of Persia, so that he made a proclamation throughout all his kingdom and also put it in writing: