 Littleton grew significantly throughout the 1950s and 1960s due to its proximity to Martin Marietta facilities, which produced the Titan rocket and other aerospace products.Littleton twinned with Bega, Australia in 1961 as one of the earliest sister cities.Littleton became widely known in 1999 when the Columbine High School massacre occurred at Columbine High School, where two of the school's students, Eric Harris and Dylan Klebold, murdered 12 students and one teacher, injured 24 others and then killed themselves.