It is the latest protest to rack Bangladesh, deepening tensions between secularists and the largest Islamic party, Jamaat-e-Islami, whose leaders are under trial for crimes committed during the country's 1971 war of independence.
The Islamists converged on Dhaka's main commercial hub to protest against what they say are blasphemous writings by atheist bloggers, defying a pro-government national strike by secular protesters –– who staged a smaller rival protest in Dhaka Saturday –– aimed at resisting the march.
Police said about 100,000 people attended the rally during which protesters chanted "God is great, hang the atheist bloggers."
Protest organizers, who called the rally the "long march" with many travelling from remote villages, put the number at more than half a million, as Dhaka's Motijheel commercial area turned into a sea of white robes.
"I've come here to fight for Islam. We won't allow any bloggers to blaspheme our religion and our beloved Prophet Mohammed," said Shahidul Islam, an imam at a mosque outside Dhaka who walked 20 kilometers (13 miles).
Hefajat-e-Islam, an Islamic group which draws support from tens of thousands of seminaries, organised the rally in support of its 13-point demand including enactment of a blasphemy law to prosecute and hang atheist bloggers.