The objective of this article is above all – on the example of two events involving Polish soldiers at Fons (May 1809) and in the Sierra Morena mountains (January 1810), howbeit not exclusively – to draw attention to the fact that when approaching the Peninsular War, the historian cannot underestimate the role of ambushes or minor skirmishes – contrary to the major open space battles (e.g. Arapiles 1812) or sieges (e.g. Saragossa 1808–09) being less scientifically accessible or intelligible due to the relative shortage of sources, which, combined with the usual lack of decisiveness, makes them an unrewarding object of examination. This underestimation lies primarily in the adoption of too broad or, paradoxically enough, too narrow a perspective – as if they could be a subject of detailed treatises only. Meanwhile, as the record shows, these guerrilla-style ambushes are a phenomenon to be considered both in detail and in general, not only for understanding individual vicissitudes but also for better explaining Napoleon’s ultimate defeat in Spain, which is too often attributed overwhelmingly to Wellington’s military genius. They also played an important role in Polish memoirs and military theory, which is to be discussed in a separate section. The choice of the above-mentioned ambushes is by no means random. First, mutually explaining and lightening each other up, Fons, Sierra Morena, and others occurred in a similar and representative period of time: neither when the Peninsular War was just developing, nor drawing to its end during and after the disastrous Russian campaign, but when it was in full swing. Secondly, despite what has been said about the majority of such clashes, and thanks to a number of sources, the historian is able to have a certain insight into those specific ambushes. Thirdly, we are about to see that their consequences cover nearly the maximum range of war occurrences that could be experienced by the Polish-Napoleonic soldiers. Fourthly, we shall learn that this type of guerilla warfare had a certain influence on the Polish national liberation movement.