Prime Minister Narendra Modi on Thursday paid tribute to the martyrs of Jallianwala Bagh massacre in Punjab, saying that their heroism will never be forgotten."Saluting the martyrs of the Jallianwala Bagh massacre. Their valour and heroism will never be forgotten," Modi tweeted.The massacre took place on April 13, 1919 when a crowd of non-violent protestors, gathered in Jallianwala Bagh, Amritsar, were fired upon by troops of the British Indian Army.