The Battle of the Tagus was a naval engagement that took place on 11 July 1831 at the mouth of the Tagus river, in Portugal. A French fleet attacked and subdued Portuguese fortifications at the entrance of the Tagus, with the aim to strong-arm the government of Miguel I into recognising the newly established Kingdom of the French. The destruction of the forts defending access to the Tagus and the arrival of French warships at Lisbon forced the Portuguese to cave in and comply with French demands.