My entry:
To keep and measure the time, has been the motivation of many advances in mathematics and technology.
One of the first techniques to measure the time was the sun dial. This photo shows a very simple sun dial (which is not in very good conditions). In spite of the fact that the photo was taken during a cloudy day, we can see the shadow of the dial and see that it is almost 11 am.
More details in this post:
https://hive.blog/hive-153349/@nenio/time-tiempo-en-es