You are confusing two terms. At the Olympic level, there is the decathlon, 10 events over 2 days:
A decathlon is, in order
Read more: What_are_the_olympic_field_events_in_the_decathlon
And the military oriented Modern Pentathlon, 5 events on one day:
cross country running.
A decathlon is, in orderDay 1100mLong JumpShot PutHigh Jump400 mDay 2110HDiscusPole VaultJavelin1500mRead more: What_are_the_olympic_field_events_in_the_decathlon
it is called a decathlon
An athletic contest of ten sports is a decathlon and a contest of three sports is a triathlon
15, not including the decathlon which has track and field sports.
A decathlon is an athletic contest consisting of 10 sports.
In the modern Olympics, 1904.
it is a decathlon.