A total of about 1,000 police officers were deployed in and around the government district of Berlin on Thursday, a spokeswoman said, in order to police the state ceremony to mark the 75th anniversary of Germany's constitution.
The police were also out on the Spree river on patrol boats and had deployed a helicopter.
The Federal Criminal Police Office (BKA) and special task forces (SEK) from the Berlin State Criminal Police Office and from Lower Saxony were also involved.
The situation was calm and relaxed in the morning, police said.
A total of 1,100 guests were expected on the square in front of the Chancellery. Among them were Chancellor Olaf Scholz, most of the ministers, many state premiers and representatives of the Bundestag and other institutions. President Frank-Walter Steinmeier is to deliver the main speech.
The Basic Law come into force on May 23, 1949, which is also the founding date of the Federal Republic of Germany.