HINTS： 

Egypt in the third century B.C. 

North African

Mediterranean Sea.

There was once a time when our little planet seemed immense when it was the only world we could explore. Its true size was first worked out in a simple and ingenious way by a man who lived here in Egypt in the third century B.C. This tower may have been a communications tower, part of a network running along the North African coast by which signal bonfires were used to communicate messages of state. It also may have been used as a lighthouse, a navigational beacon for sailing ships out there in the Mediterranean Sea.

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