flames on the wooden roof. In 1986, a new Martyrdom Altar was installed in the northwest transept, on the spot where Thomas Becket was slain, the first new altar in the cathedral for 448 years. Mounted on the wall above it, there is a metal sculpture by Truro sculptor Giles Blomfield depicting a cross flanked by two bloodstained swords which, together with the shadows they cast, represent the four knights who killed Becket. A stone plaque also commemorates Pope John Paul II's visit to the United Kingdom in 1982. Antony Gormley's sculpture Transport was unveiled in the crypt in 2011. It is made from iron nails from the roof of the south-east transept. In 2015, Sarah Mullally and Rachel Treweek became the first women to be ordained as bishops in the cathedral, as Bishop of Crediton and Bishop of Gloucester respectively. In 2022, it was announced that David Monteith, who is openly gay and in a civil partnership, would serve as Dean of the Cathedral. The cathedral is Regimental Church of the Princess of Wales's Royal Regiment and a graduation venue for the University of Kent and Canterbury Christ Church University. Conservation Much of the stonework at Canterbury Cathedral is damaged and crumbling, the roofs are leaking and much of the stained glass is badly corroded. The last quinquennial structural review revealed that a combination of centuries of weathering, pollution and constant use had taken its toll on the ancient building and some serious problems were in need of urgent action. The single biggest challenge is the roof. The cathedral is covered by a huge expanse of lead and whilst the majority of the wooden framework remains sound, much of the lead itself needs replacing. In addition, a large amount of concrete encasing the bottom of the roof beams needs to be removed and replaced with traditional wooden footers. Conservation of the external masonry, particularly on the northern side of the building, is equally important. The cathedral is in part built of Caen stone. Detailed archaeological studies are undertaken to identify exactly which stones need to be replaced or repaired. In addition, specialist cleaning techniques are used to remove accumulated chemical deposits which are very damaging to the building. As regards the interior, priorities include decoration of the vaults of the Trinity Chapel, conservation work in several other chapels, and major improvements to the Treasury building, which contains, amongst other