‘Weimar is Germany in a nutshell,” 1990s president Roman Herzog once quipped: “a town in which not only culture and thought were at home but also philistinism and barbarism.” The small city (population 65,000) sits at the heart of the nation and acts as a shrine to its sons Goethe, Schiller and Nietzsche. In 1919 the country’s first democratic constitution was promulgated in its national theatre. It was chosen as the site of Germany’s rebirth precisely because its aura of refined culture contrasted so sharply with the “Prussian militarism” of Berlin. From 1919-1925 it hosted the Bauhaus School, led by Walter Gropius, placing it at the forefront of art and design.

Yet, starting in the mid-1920s, Weimar, which was also then the state capital of Thuringia, became pivotal in the rise of the Nazi party and its first, regional, experiments in government. After 1933 it competed with Bayreuth for recognition as the “spiritual home of Nazism”.

Historian Katja Hoyer, best known for 2023’s Beyond the Wall, evokes some of these dissonances in her new work charting Weimar’s interwar story. She divides the book into chapters chronicling local events every year between 1919 and 1939, blending public records with personal letters, diaries and memoirs left by the city’s inhabitants.

In this chronology, 1926 is the hinge. This was the year Weimar hosted a Nazi congress on the weekend of 3-4 July, the first rally since the party’s re-foundation in 1925, following 14 months of prohibition. It was a modest affair: police estimated there were 7,000-8,000 attendees. Yet, the gathering established core elements of Nazism, including the Hitler Youth.

On the Sunday morning, in the auditorium where the Weimar constitution had been agreed seven years before, Hitler instigated the “Blood Flag” ritual. Newly formed SA Stormtrooper units marched across the stage, consecrating their standards by touching them to a party flag carried during the 1923 Munich putsch, and allegedly stained with a fallen SA man’s blood. Hoyer writes: “In the cradle of Germany’s post-war democracy, Hitler performed a ceremony to sanctify a movement intent on killing the young republic.”

The Nazis didn’t make a favourable impression in the town. Over two days they left a trail of damage and injury behind them: breaking into cars; vandalising buildings, knifing locals and shooting a policeman. Yet by 1929, amid renewed economic crisis, Weimarers felt differently. In that December’s state elections 11% of Thuringians voted for the Nazis, but in Weimar the share was 24%.

Coming in third, they entered government for the first time, in coalition with other rightist parties. They took control of the state ministries of the interior and of education. Until the coalition’s collapse in 1931, Thuringia in general, and Weimar in particular, became a laboratory for Nazi government.

The year 1937 was Weimar’s darkest before the war, with the establishment of Buchenwald concentration camp, Germany’s largest, only five miles from the city centre. Camp and town were intertwined. Prisoners arrived at Weimar’s railway station. Local authorities provided utilities and services including, until 1940, use of the municipal crematoria to burn bodies. Although officially a work camp, not an extermination camp, it would claim the lives of 56,000 (mainly Jewish) inmates.

Weimar businesses supplied food and materials to maintain the camp while locals enjoyed access to the zoo set up to entertain guards and their families. Surreally, despite Nazi abhorrence of Bauhaus, the sign over the camp’s gate “Jedem Das Seine” (“To Each His Own”) was executed in one of the school’s elegant typefaces by a Bauhaus graduate and Buchenwald inmate, Franz Ehrlich.

Hoyer’s abhorrence of the Third Reich is obvious, but she is reluctant to criticise the ordinary people whose archival traces lend her work colour: “it is difficult and often unhelpful to judge people’s behaviour from our vantage point a century later”. Yet her book confronts us with many troubling ambiguities.

One example is that of the stationery shop owner Carl Weirich, Hoyer’s most quoted voice. After repeated near bankruptcies caused by economic turmoil, Carl voted for the Nazis in 1933. In 1934-5 he was even a financial supporter of the SS. Yet, he was never a formal party member, and by 1938 his diary betrays unease. Following Kristallnacht, he noted that “increasing persecution of the Jews began which blasphemed against God himself”.

Weirich’s diary records with horror the sight of crematoria and piles of corpses at Buchenwald when he and other Weimarers were shown them by American troops following liberation. Not once, however, in a journal lasting up to the 1970s, does he question what part his own choices might have played in bringing those atrocities about.

Though she eschews judgment on individuals, Hoyer nevertheless writes with moral purpose. Understanding why ordinary, even likable, people turned away from democracy in the past is, she argues, essential to safeguarding freedom in the present. Given that Thuringia’s last state elections in 2024 witnessed another far-right breakthrough, with the AfD topping the poll on 33%, that task could scarcely be more urgent.

Weimar: Life on the Edge of Catastrophe by Katja Hoyer is published by Allen Lane (£30). To support the Guardian order your copy at guardianbookshop.com. Delivery charges may apply.