In June 1812, Napoleon invaded Russia. On 22 June, 139 years to the day before Hitler’s invasion of the USSR, he issued a proclamation to his soldiers, telling them that ‘The second Polish war has opened; the first ended at Friedland and Tilsit.’ Europe, apart from the Iberian Peninsula, had been at peace since 1809. See this post for the situation in the Napoleonic War in June 1812.
On 22 June Napoleon’s Polish lancers reconnoitred the west bank of the River Niemen for any sign of Russian troops on the far bank. At night Napoleon, wearing a Polish uniform, personally led a small party across the river, looking for the best place to cross. He was thrown from his horse after a hare caused it to shy.
Marshal Louis-Alexandre Berthier, his chief of staff, told General Armand Caulaincourt, formerly Napoleon’s ambassador to Tsar Alexander I, that ‘We would do well not to cross the Niemen. This was a bad omen.’ Caulaincourt, who had advised Napoleon against attacking Russia, commented that the Emperor ‘remained very serious and preoccupied for the rest of the day.’
The rest of 23 June was taken up with preparations for the crossing. Light infantry crossed by boat at 10 pm in order to screen the construction of three pontoon bridges by engineers. They were briefly fired on by a Russian cavalry patrol, but this was the only resistance offered to the crossing; the Russian army had withdrawn. The bridges were completed by dawn and the Grande Armée crossed on 24 and 25 July.
The Grande Armée was a huge, multi-national force. David Chandler puts its strength at 614,000, including 302,000 Frenchmen, 190,000 from Austria, Prussia, Switzerland and other German states, and 90,000 Poles and Lithuanians. The remaining 32,000 were Italians, Illyrians, Spaniards and Portuguese. The enthusiasm of many, other than the French and the Poles, was questionable.
Three armies, totalling 449,000 men formed the main invasion force. The other 165,000 men were intended mainly to provide replacements. Napoleon had previously commanded armies of no more than 200,000 men.
He had 1,422 cannons, pulled by 30,000 horse, and 80,000 cavalry. The supply train included 25,000 vehicles and a further 90,000 animals. Supplying such a large army was a major problem, and Napoleon timed the invasion for the point at which the grass crops would provide the most animal feed. 
The invading force heavily outnumbered the Russian forces facing it. Chandler says that the Russian Army had 409,000 soldiers in early 1812, of whom 211,000 were in front-line armies, 45,000 in the second line and 153,000 in garrisons and reserve units. By June 1812, transfers from the quiet Turkish and Persian fronts and from garrisons and reserves had allowed the formation of three Russian field armies in the west with 218,000 men by June 1812.
Napoleon had, by invading Russia, launched an enormous enterprise. Charles Esdaile notes that the ‘”The great proof of madness”, Napoleon is once supposed to have said, “is the disproportion of one’s designs to one’s means.” If so, then the Emperor stands condemned from his own mouth.’
The next post in this series will consider the reasons why Napoleon decided to invade Russia, which had been his ally since the Treaty of Tilsit in 1807.
 Quoted in D. Chandler, The Campaigns of Napoleon (London: Weidenfeld & Nicolson, 1966), p. 739.
 Both quoted in A. Zamoyski, 1812: Napoleon’s Fatal March on Moscow (London: HarperCollins, 2004), pp. 146-47.
 Figures in this and the two previous paragraphs are from Chandler, The Campaigns of Napoleon, pp. 753-59.
 Ibid., pp. 750, 764.
 C. J. Esdaile, Napoleon’s Wars: An International History, 1803-1815 (London: Allen Lane, 2007), p. 401.