As the practice grew in the 20th century, it required additional space. Saint Marys Hospital underwent frequent expansion. Rochester business leader John Kahler built innovative hotel-hospital facilities that served Mayo Clinic patients. In 1914, Mayo Clinic opened the world's first building expressly designed for multispecialty group practice, known as the 1914 "red brick" building. It facilitated ease of movement for patients and staff among specialty areas, brought research and education functions into proximity with clinical practice, and patient amenities. This approach was replicated and enhanced with the adjoining 1928 Mayo Clinic building, later named for Dr. Plummer, its principal designer, which is listed on the National Register of Historic Places. The Plummer Building features bronze entry doors designed by artist Charles Brioschi. Each 16-foot high, 5.25-inch thick door weighs 4,000 pounds and features ornamental panels. The doors are closed to memorialize important historical events and influential people, such as the deaths of the Mayo brothers, the assassination of President John F. Kennedy, and the victims of September 11, 2001 terrorist attacks. The 1914 "red brick" building, a National Historic Landmark, was demolished by Mayo Clinic in the 1980s to make way for the Siebens Building (completed in 1989). Mayo Clinic's campus has undergone expansion over the years.