In this task, you are given a question and a context passage. You have to answer the question based on the given passage.
One example: what is the first event mentioned?, Context: The Russian Revolution is the series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. Following the abdication of Nicholas II of Russia, the Russian Provisional Government was established. In October 1917, a red faction revolution occurred in which the Red Guard, armed groups of workers and deserting soldiers directed by the Bolshevik Party, seized control of Saint Petersburg (then known as Petrograd) and began an immediate armed takeover of cities and villages throughout the former Russian Empire.
Solution is here: Russian Revolution
Explanation: This is a good example, and the Russian Revolution is the first event mentioned.

Now, solve this: When was the manipular formation first used?, Context: One disadvantage of the phalanx was that it was only effective when fighting in large, open spaces, which left the Romans at a disadvantage when fighting in the hilly terrain of central Italian peninsula. In the 4th century BC, the Romans abandoned the phalanx in favour of the more flexible manipular formation. This change is sometimes attributed to Marcus Furius Camillus and placed shortly after the Gallic invasion of 390 BC; it is more likely, however, that they were copied from Rome's Samnite enemies to the south, possibly as a result of Samnite victories during the Second Samnite War (326 to 304 BC).
Solution:
shortly after the Gallic invasion of 390 BC