Hours earlier in Brussels, Erdogan had reached a historic deal taking Turkey one step closer to its decades-old dream of European Union membership.
But the hard work, he told the crowd, is only just beginning: "This result should not relax us. We must work harder [and] from now on we will work more, but we [the government] will not work alone, we [everyone] will work all together."
The 17 December deal had nearly collapsed over the difficult issue of Cyprus. The island is split between the north -- where Turkey still has troops -- and the Greek Cypriot south, a new EU member.
The EU asked Turkey to immediately sign a key protocol including Cyprus in its customs union. Erdogan refused, saying this amounted to tacit recognition of the Greek Cypriot government.
But finally, after hours of negotiation, a compromise was reached. Erdogan agreed to sign the protocol -- but just not yet. Ankara now has until the accession talks begin in October to do so.
On 18 December, much of the press was hailing the deal as a victory, and giving Erdogan the credit. "We Did It," was the headline in the mass-circulation "Hurriyet." Another daily, "Posta," said "You Are Great, Turkey."
But there was criticism, too. The daily "Yeni Cag" said Turkey had been dishonored. This was the response of two men on the streets of the Turkish city of Biyarbakir: "Well, the existence of the EU will make the peoples lives better, if so that is a good thing. If we will be able to implement the new regulations to our lives then the EU will mean something, but if these criteria remain on the paper then it means nothing for us."
The deal does not guarantee Turkey will become a member of the EU. Turkey's entry is still strongly opposed in several EU countries, whose citizens fear an influx of migrants from a different culture who would compete for jobs.
Accession talks are likely to run a decade or so, and Turkey will also have to transform its economy, society, and politics.
But if it does join the EU, it will be the bloc's first predominantly Muslim member state -- and bring Europe's political borders up to Iraq, Iran, Syria, and the Caucasus states of Armenia, Azerbaijan, and Georgia.