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.
... 190s 200s 210s 220s 230s - 240s - 250s 260s 270s 280s 290s Years: 237 238 239 240 241 - 242 - 243 244 245 246 247 Events Patriarch Titus[?] succeeds ...