Lambasting Turkey's enemies and taking pot shots at his opponents, Erdogan said a 'Yes' vote in the April 16 referendum would give the country more stability and power.
"On April 16, do you want to say 'Yes' to a strong Turkey?" Erdogan asked the crowd, who waved a sea of red and white crescent moon Turkish flags.
"Do you want a great Turkey? Do you want to say 'Yes' to stability? Will you be there Istanbul?" he added, as the crowd roared back 'Yes!".
Erdogan arrived by helicopter to cheers at the vast open ground in Istanbul's Yenikapi district, on the shores of the Sea of Marmara.
It was here last August that he held a mass rally calling for national solidarity in the wake of the failed July coup blamed on the US-based preacher Fethullah Gulen, and Erdogan clearly wanted to capture the spirit of that day.
Erdogan said the likes of Gulen, who denies being behind the coup, and the outlawed Kurdistan Workers Party (PKK) wanted to see a 'No' vote.
And he charged that 'No' voters were also against his bid to transform Turkey through modern infrastructure projects such as bridges and tunnels.
"They said 'No' to the bridges. They say 'No' to a modern Turkey," he roared, prowling around a walkway that extended from the stage like at a rock concert.
'Turkey not herself without Erdogan'
Analysts see the referendum as tightly contested, despite the domination of the 'Yes' campaign in the media.
If approved, the new system will see the scrapping of the post of prime minister, the creation of vice presidents and the empowering of the president to appoint ministers.
The changes will also allow the president to be affiliated with a party, allowing Erdogan to restore his ties with the Justice and Development Party (AKP) that he co-founded and helped sweep to power in 2002.
Supporters say the new system will create an efficient US-style structure but critics argue the lack of checks-and-balances risks handing Erdogan one-man rule.
Wearing headbands with "Tayyip Erdogan -- commander in chief" written on them and some even sporting Erdogan face masks, supporters said giving the president greater powers was essential to Turkey's development.
"We want Turkey to grow, we want Recep Tayyip Erdogan to remain our leader. Without him Turkey is not herself," said 'Yes' supporter Nahil Unal.
Erdogan also prompted boos by mentioning his opponent, the leader of the secular Republican People's Party (CHP) Kemal Kilicdaroglu, who claimed this week that the failed putsch was a "controlled coup" which the government knew about in advance.
Analysts say that the outcome in Turkey's largest city Istanbul -- whose diversity is fairly representative of the hugely complex country -- will be critical to the result of the referendum.
The 'No' campaign suffers from a lack of a clear figurehead and vastly fewer resources but is hoping to rally substantial numbers of secularists, Kurds and nationalists to its cause.
On the other Asian side of the city across the Bosphorus, the pro-Kurdish Peoples' Democratic Party (HDP) held a rally pushing a 'No' vote.
Both the party's co-leaders are jailed on charges of backing the PKK, which the party argues is punishment for daring to oppose the presidential system.
Senior HDP lawmaker Sirri Sureyya Onder told the rally: "In this referendum our co-leaders, our MPs, our youth, our friends are facing the greatest oppression in our history."
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