The Serpents Island has always had a strategic position in relation to the navigation to/from the ports of the Danube and those on the Ukrainian Black Sea coast. Since the 1830s, when the imperial Russian authorities built a lighthouse on the island, it became an even more visible landmark for the increasingly numerous commercial ships heading to local ports. At the end of the Crimean War, the Serpents Island was the object of a serious diplomatic conflict between the European powers, a dispute which, together with the delimitation of the southern Bessarabian border, complicated and delayed the execution of the terms of the 1856 Paris Peace Treaty. As the treaty did not mention anything about the island’s status, Russia claimed that it had remained under its sovereignty, while the Ottomans considered that it should return to the Porte, being linked to the control of the Danube Delta. Britain supported the Ottoman claim, while France had a more ambivalent position, in line with the ambitions of Napoleon III, towards what appeared to be an unimportant rock in the Black Sea. The diplomatic episode was analysed, based on different sources, by several historians. Starting from a collection of British documents, this paper aims to detail how the Serpents Island question evolved in 1856 from both a diplomatic and strategic perspective. In 1857, when the Treaty of Paris was amended, the island was granted to the Ottoman Empire, which also took over the administration of the lighthouse. This paper also includes ten unpublished sources regarding the history of the Serpents Island.