Kemal Kilicdaroglu, who underperformed in the first round after finishing second to Erdogan, has hardened his stance on migration to win over voters. Will it pay off?
Sinan Ogan has emerged as a potential kingmaker after neither Erdogan nor his main challenger secured an outright majority in the first round.
The Turkish president is trailing in the polls ahead of Sunday's presidential contest.
The march is the biggest protest yet against the crackdown that followed last year's failed military coup.