Standing on the stage of Mainz's Rheingoldhalle auditorium, President Frank-Walter Steinmeier looked back on October 3, 1990 — the date when the former East and West Germany officially reunited — but also cast his gaze forwards at the path the nation now faces following the national election's outcome just nine days prior.

"The large wall that ran across our country is gone," Steinmeier said, referring to the Berlin Wall and the inner German border that had divided the German Democratic Republic (DDR) and the Federal Republic of Germany (BRD). "But on September 24, it became clear that other walls have arisen, less visible ones, without barbed wire and death-strips, but walls that stand in the way of a unified 'we.'"

Read more: German reunification: Are youth in love or indifferent?

The president's speech, aired in English on DW TV, marked the 27th anniversary of Germany's peaceful reunification. The day's official celebrations took place in the city of Mainz, where some 500,000 guests were expected including German Chancellor Angela Merkel and Norbert Lammert, the outgoing president (speaker) of the Bundestag.

Work for further unity lies ahead

Steinmeier focused much of his speech on appeals to Germany's younger people and voters, a growing contingent of whom have only known a reunified Germany. "Germany is unified every day" nowadays, Steinmeier noted, saying: "What we're celebrating today is something ordinary — but by no means something that's a given." He even advised those who never knew a divided Germany to "ask the people who were there."

He also alluded to the upcoming formation of a new parliament that will include the right-wing Alternative for Germany (AfD).

"The German Bundestag that was elected nine days ago will be different. It reflects the clearer-cut opposition and also the dissatisfaction that exists in our society. The debates will be rawer, the political culture will change," Steinmeier said, before calling on politicians to show that solutions come from those who support democracy rather than those who disparage it.

Read more: Opinion: German unity has become a mission again

Steinmeier also sought to acknowledge some errors during Germany's reunification process, with the Social Democrat saying that "mistakes were made in the years after 1990."

"After reunification, East Germans lived through fractures that our generation in the West [Germany] never knew," he said, adding that this East German history needed to become part of Germany's common understanding of itself.

The president's words touched on the ongoing divide between Germany's two former states that was once again thrown into the analytical spotlight with the AfD's significantly better outcome in the former DDR regions than in the former BDR. He warned that the concept of a home or homeland must not be left to the far-right to define in a nationalist manner.

Throughout his speech, Steinmeier — a veteran who most recently served a second stint as foreign minister — rooted Germany in the European community. He also called for a national discussion on migration, one of the main election issues, and added that this would mean creating new guidelines to differentiate between politically persecuted individuals and economic migrants.

The chancellor from the East

Merkel also weighed in during the festivities in Mainz. The chancellor, who grew up in former East Germany, said the anniversary was a "day of joy" for the country and that there was a responsibility to uphold freedom at home and abroad. "We know we cannot disconnect from what's going on in the world. Rather, we must take care that globalization is constructed humanely," she said in remarks made during the festivities in Mainz.

Merkel's conservative Christian Democrats (CDU) won the most votes in Germany's September 24 national election, securing the chancellor a fourth term as head of government.

Read more: Angela Merkel warns against east-west division over AfD rise

Festivities and security in Mainz

Merkel received a far warmer welcome in Mainz than she did in Dresden one year prior, where she was greeted with boos and protests. German radio broadcaster SWR reported that some 150 protesters were present in Mainz to voice opposition to the national celebration.

The official Day of German Unity celebrations take place in a different German city every year, part of a bid to include the entire reunified country in the festivities. This year, the Mainz celebration took place under the motto "Together we are Germany."

On Tuesday before Steinmeier's speech, some 1,000 guests, including German politicians, attended an ecumenical service in the Mainz cathedral. A total of 4,300 police officers were deployed in Mainz to secure the streets and keep order in the city, the capital of the state of Rhineland-Palatinate.

Each of Germany's 16 states were on display at the public events, as was a large replica of Berlin's Brandenburg Gate, at a festival near the banks of the Rhine River. Later in the afternoon, festival-goers gathered together to take part in a new national holiday tradition by singing a round of "Ode to Joy," the Freidrich Schiller poem used (with some alterations) by Ludwig van Beethoven in his 9th Symphony, which has since been adopted by the EU as Europe's anthem. A light and music show on the Rhine was set to bring the day's events to a close.

Celebrations in Mainz began on Monday with several concerts including performances from German pop star Tim Bendzko and eastern German rock band Karat.

Celebrating a reunited Germany across the country

As part of Germany's national holiday, 1,000 mosques around the country also opened up their doors to visitors, including a mosque in Cologne belonging to Germany's largest Islamic organization, DITIB.

Read more: Islam in Germany: Muslims prefer to be talked to rather than talked about

Germans celebrated Unity Day in other cities across the country, with some taking advantage of the nationwide day off from work to participate in municipal events, such as Berlin's food and music festival around the Brandenburg Gate.

And even those who stayed home and went online had the chance to celebrate with the Google Doodle for the day. The side-by-side Volkswagen Beetle and East German Trabant, or "Trabi," greeted internet users on Tuesday.

The international community also took note of the anniversary celebrations. Russian President Vladimir Putin sent a congratulatory message to Steinmeier and Merkel. In a press release on the presidential website, Putin stated that the long legacy of Russian-German relations is of "great importance" and voiced a commitment to working for European and world security and stability.