According to the Oxford Dictionary, the term Chronology is defined as
"The science of computing and adjusting time or periods of time, and of recording and arranging events in the order of time; computation of time, assignation of events to their correct dates."
And a Timeline is
"A line used to illustrate or represent a chronological sequence of events; a chronology; a chronological sequence."
------------------------------------------------------------------------
Key words here are order and represent.
Historical thinking entails establishing the order of events (the chronology) and historians represent this order by using timelines. When historians create timelines they are identifying certain events as important and representing these events on the timeline.