English to Chinese Social Sciences History

The Ring is a circle of beech trees, planted on a hilltop that had been the site of Bronze Age and Iron Age fortifications, and a Roman temple. In 1760, a young aristocrat from the scarp-foot village of Wiston named Charles Goring decided to add his own layer of history to the Chanctonbury earthworks. He planted beech saplings in a well-spaced circle and, according to one story, then carried bottles of water up the slope to irrigate his saplings daily on that arid summit. According to the other story, he got his servants to do this job for him.如何理解layer of history？