Colons are commonly used to introduce lists, or to connect a broad idea with a specific example: two related sentences can be separated by colons instead of periods.
... 19th century - 20th century - 21st century Decades: 1850s 1860s 1870s 1880s 1890s - 1900s - 1910s 1920s 1930s 1940s 1950s Years: 1899 1900 1901 1902 1903 - ...