Every 200 years.
look up the definition of bicentennial
Every 200 years.
Every 200 years
A bicentennial is the 200th anniversary of anything. For example, the American Bicentennial was 1976, the bicentennial of Abraham Lincoln's birth is 2009.
Bicentennial or bicentennially
A bicentennial day is the 200th anniversary of a significant event (often the founding of a city), so the one specified celebrates something that happened on April 30, 1812.
Bicentennial means "200th anniversary".
Bicentennial
Bicentennial means 200 years old. We celebrated our country's bicentennial last year.
A bicentennial celebrates 200 years of something.
Bicentennial Tower was created in 1996.
We celebrated the bicentennial anniversary of the birth of our country