If not anything, the flash mob did manage to make the day of the commuters and that's what counts. Awesome guys!

It is believed that the flash mob was organized as a promotion for the film 300:

What would've otherwise been just like any other day for the passengers of the London Underground changed for something spectacular when they witnessed a group of spear-wielding, leather-clad "Spartans" parading the streets and the subway stations of London. The flash mob, inspired by the famous film 300, were pictured having a gala time attracting all the attention from commuters. 

It is believed that the flash mob was organized as a promotion for the film 300: Rise of the Empire releasing on DVDs.

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If not anything, the flash mob did manage to make the day of the commuters and that's what counts. Awesome guys!
Source indiatimes