Births on October 11

Gregor von Helmersen, Estonian-Russian general and geologist (d. 1885)

Gregor von Helmersen (11 October [O.S. 29 September] 1803 – 15 February [O.S. 3 February] 1885) was a Baltic German geologist.

18 May

Treaty of Amiens
Napoleonic Wars: The United Kingdom revokes the Treaty of Amiens and declares war on France.
23 Sep

Battle of Assaye
Second Anglo-Maratha War: Battle of Assaye between the British East India Company and the Maratha Empire in India.
20 Oct

Louisiana Purchase
The United States Senate ratifies the Louisiana Purchase.