Meanwhile, on October 22nd, when Russia and Turkey were already at war, the fleets of England and France entered the Dardanelles. Though this was not an infraction of the treaty of 1841, it was a distinctly hostile act on the part of these Powers against Russia. But negotiations still continued. Whatever hopes, however, there were of a favourable issue were destroyed when, on November 30th, a Russian fleet of six battleships, issuing from Sebastopol, attacked and completely destroyed a Turkish squadron of eleven cruisers and smaller vessels lying at anchor in the port of Sinope, on the coast of Asia Minor. Four thousand Turkish sailors perished in this engagement. This was an act of war, as legitimate as the attack by the Ottoman army on the Russian force north of the Danube, the more so as the Turkish vessels were believed to be carrying munitions of war to arm the Circassians against Russia. It caused, however, an immense sensation in England and France. It was denounced as an act of treachery and as a massacre rather than a legitimate naval action. The fleets of the two Powers then lying in the Bosphorus were at once instructed to enter the Black Sea and to invite any Russian ships of war they might meet there to return to their ports. They were to prevent any further attack on Turkey. This made war inevitable. But negotiations were still for a time continued, and it was not till March 28, 1854, that war was actually declared against Russia by England and France. Armies were then sent by these Powers to Constantinople, and thence to Varna, in the Black Sea, with the object of protecting Turkey against the attack of a Russian army and of assisting the former in compelling the evacuation by the Russians of the two Danubian provinces. Meanwhile, early in the spring of this year (1854), a Russian army had crossed the Danube and had invested Silistria, the great fortress which barred the way to the Balkans and Constantinople. It was defended with the utmost bravery and tenacity by a Turkish army under Moussa Pasha, assisted by two British engineer officers, Butler and Nasmyth. On June 25th the Russians recognized that they could not capture the fortress. They raised the siege and retreated across the Danube, after incurring immense loss of life and material.