On 3 September 1967, Sweden executed one of the most ambitious peacetime logistical operations in modern history: switching from left-hand to right-hand traffic in a single morning. Dagen H, as it was known, required years of planning, military coordination, and the cooperation of 4.5 million drivers. Clare Vale explores how this audacious plan worked, why accident rates actually dropped afterwards, and what it reveals about collective trust. The episode also visits the traditional founding date of San Marino in 301 CE, the world’s oldest surviving republic, examines the 2017 discovery of a Second World War bomb that forced 60,000 people to evacuate Frankfurt, and revisits the launch of eBay on 3 September 1995, allegedly beginning with the sale of a broken laser pointer to a collector. Four stories about human ambition, persistence, unfinished history, and the odd logic of markets.