What is the importance of Hangman's Hill in the novel, The Last Apprentice (Revenge of the Witch)?

Hangman’s Hill is located right near Tom’s farm, and he has to pass through it on his way to Horshaw. At a young age, Tom was bothered by the spirits that inhabited Hangman’s Hill. There are hundreds of spirits of soldiers that had been executed during a previous war. Tom’s mother eventually silences the spirits, something that seems to be above even Gregory’s skills.