The Romans built the fort of Almus (from where the name of the today's city and of the Lom River comes) on the Danubian Limes frontier system along the Danube.

It was not until Ottoman rule that it enlarged but for a long time it was under the shadow of the dominant towns of Vidin, Nikopol and Silistra.

It is assumed that the Ottoman village was founded in 1695 by Kara Mustafa[dubious – discuss] and Murad Giray,[clarification needed] who were defeated at Vienna in 1683 and who came here sailing rafts along the Danube.

At the time, the name palanka was used for settlements that stood between village and city (grad) in size and importance.

The town was centred on the old Kale (fortress), which was entered through three kapii (gates), each named after the place that the respective road led to - Vidin, Belogradchik, Sofia.

In 1943, the Bulgarian government transported several thousand Jewish captives from Bulgarian-occupied territory in Greece and Yugoslavia to Lom to be embarked on boats bound for Vienna in Nazi Germany, from where they were taken to be exterminated in Treblinka.