LONDON — Britain is celebrating its longest-reigning monarch, Queen Elizabeth II, in her Platinum Jubilee year.

The 96-year-old queen is being toasted across the nation with four days of events showcasing the best of British pomp and pageantry. Crowds in London will try to catch a glimpse of royal family members on the Buckingham Palace balcony, while others will attend concerts and street parties or simply enjoy the national holiday.

Here’s everything you need to know about the celebrations.

What is the Platinum Jubilee?

The Platinum Jubilee marks Elizabeth’s 70th year on the throne. She is the first British monarch to reach that milestone. Her great-great-grandmother Queen Victoria was the previous longest-serving monarch, reigning for 63 years before her death at age 81 in 1901.

Queen Elizabeth II: A visual timeline of her 70 years on the throne 

Let’s back up. What even is a jubilee?

A jubilee is an anniversary celebration with Judeo-Christian origins that was adapted to mark milestones of a British monarch. The third book of the Old Testament, Leviticus, tells people to “sanctify the fiftieth year … for it is the year of jubilee.”Records from the 14th century show that King Edward III celebrated 50 years on the throne, his Golden Jubilee, with a week-long joust and a procession from the Tower of London. But many of today’s jubilee traditions can be traced to the reign of King George III, best known for his poor mental health and for losing the American colonies. The beginning of his 50th year on the throne was marked with church services, feasts, fireworks and souvenirs.