On the evening of June 20, 1996, a running battle is fought between members of the D.A. led by Harry Potter, a group of Death Eaters led by Lucius Malfoy, and members of the Order of the Phoenix. Sirius Black is killed and many others are wounded (OP35). When Voldemort himself arrives and battles Dumbledore in the Atrium, Minister of Magic Cornelius Fudge is forced to admit that Voldemort has indeed returned and remove Umbridge from Hogwarts (OP36). After the battle, Dumbledore returns to Hogwarts and reveals to Harry the contents of Trelawney’s first prophecy (OP37).
June 20, 1996
Death Eaters cornered a group of Hogwarts students in the Hall of Prophecy after the teenagers had been lured there by Lord Voldemort. The students were led by Harry Potter while the Death Eaters were under the direction of Lucius Malfoy. The students, who were part of the group called the DA, or Dumbledore’s Army, suffered numerous injuries in a running battle through the various rooms of the Department of Mysteries but inflicted damage on their enemies as well. However, they had nearly been defeated when a contingent from the Order of the Phoenix arrived and turned the tide of battle in the Death Chamber. Finally, Dumbledore arrived and captured nearly all the Death Eaters. Lord Voldemort himself then Apparated into the Ministry of Magic, unaware that his archnemesis was present, and he and Dumbledore fought a tremendous duel in the Atrium. Voldemort was defeated in this duel and fled with Bellatrix Lestrange. Many were wounded on both sides and Sirius Black of the Order of the Phoenix was killed (OP34, OP35, OP36).
Harry Potter (Leader)
Order of the Phoenix
Sirius Black (killed)
Lucius Malfoy (leader)
The date of the battle was given on Pottermore as the 18th, which listed the date of Sirius Black's death. However, this information was not written by Rowling and since it doesn't agree with the other available information about the events of the spring of 1996, we don't accept it. Instead, as always in such cases when no canon information gives direction, we use the Real World calendar to place the dates of events. On that calendar, the first week of the OWLs is June 10 through 14 and the second week is June 17 through 20, which is a Thursday and the date of their last exam. The Battle of the Department of Mysteries takes place on that Thursday evening, the 20th of June.