The rally came a day after Erdogan's government rejected a warning from the military over the country's disputed presidential election, calling its interference unacceptable.
Abdullah Gul, Turkey's foreign minister and election candidate for the ruling Justice and Development Party (AKP), said on Sunday he would not withdraw his candidacy after he failed to win a first-round victory in a parliamentary vote on Friday.
"We have seen this theatre many times... [there is] no way other than democracy"
Srimedya, Bursa, Turkey
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"It is out of the question for me to withdraw my candidacy in any way," he said.
Although Gul is the sole candidate in the election, he missed out on election in Friday's vote due to a boycott by opposition groups who object to Gul's alleged Islamist past.
The result of the vote prompted a military statement that some interpreted as a robust defence of Turkey's secular character.
Gul said his decision to run for the presidency was "taken in a night" but the result of lengthy negotiations.
The main opposition Republican People's Party has asked the constitutional court to cancel Friday's vote, arguing that the session of parliament was inquorate.
If the court agrees, general elections set for November 4 could be brought forward.
If not, Gul could be president in a third round vote on May 9, when he needs only an absolute majority in the AKP-dominated parliament.
The prospect of Gul as president has alarmed secularists who suspect the AKP of having a secret Islamist agenda.
The ruling party argues that it is now committed to secular principles.