When and how did the first modern clocks develop?

In Europe during most of the Middle Ages (roughly 500 to 1500 C.E.), simple sundials placed above doorways were used to identify midday and four “tides” (important times or periods) of the sunlit day. By the tenth century, several types of pocket sundials were used. One English model even compensated for seasonal changes of the Sun’s altitude. Then, in the first half of the fourteenth century, large mechanical clocks began to appear in the towers of several large Italian cities. Historians do not have any evidence or record of the working models that preceded these public clocks, which were weight-driven. Another advance was the invention of spring-powered clocks between 1500 and 1510 by Peter Henlein of Nuremberg. Replacing the heavy drive weights permitted smaller, portable, clocks and watches. Although they ran slower as the mainspring unwound, they were popular among wealthy individuals due to their small size and the fact that they could be put on a shelf or table instead of hanging on the wall or being housed in tall cases. These advances in design were precursors to truly accurate timekeeping.