On 21 May 1849, the same day as the capture of Buda, the two emperors Franz Joseph I of Austria and Tsar Nicholas I of Russia signed the final treaty in Warsaw, which agreed on the intervention in Hungary of 200,000 Russian soldiers (and an 80,000-strong reserve force, if necessary), in order to help the Austrian Empire crush the Hungarian revolution.

[3] One was to march on Pozsony and Vienna, in order to force the enemy to fight on their own ground; the other was to return eastwards to retake Buda Castle, which was held by a strong imperial garrison of 5,000 men under the command of Heinrich Hentzi.

[3] The Hungarian staff understood that without taking the castle, the main army could not campaign towards Vienna without putting the country in grave danger and that at that moment it was impossible to achieve victory against the numerically and technologically superior imperials gathered on the Western border of Hungary.

This indicates that the arguments of those historians who wrote that Görgei made a mistake by not continuing the attack towards Vienna, because he had a great chance to take the Austrian capital and win the war before the Russian intervention,[8][9] are wrong, and at that moment (before the arrival of the Hungarian reinforcements from the south) the only place which could gain a victory was the Castle of Buda.

He ordered Jelačić to remain in Pest for a while, and then to retreat towards Eszék, in Bácska, where the Serbian insurgents allied with the Austrians were in a grave situation after the victories of the Hungarian armies led by Mór Perczel and Józef Bem.

But the imperials understood the importance of holding the Castle of Buda as long as they could, both for political and symbolic reasons as well because of having accumulated a large store of military equipment there; and they did not want to give all of these up so easily.

[27] When the victorious Hungarian Spring Campaign began, especially after their defeat in the Battle of Isaszeg, the imperial commanders started to be more and more concerned about the defence of the capitals and of Buda Castle.

[29] Hentzi thought that the cannon in the 1st to 4th rondellas (the circular bastions) needed almost no protective entrenchments; that the gates were well protected by the artillery, which could easily prevent the positioning enemy artillery before them; that the curtain wall of the castle was so strong that 12-pounder cannon could not damage it, so it was unnecessary to make earth revetments around it; that an enemy attack on the Chain Bridge could easily be stopped with gunfire; that there was no need for shell-proof shelters, because the Hungarians had no mortars; and that Svábhegy was too far from the castle to be dangerous, as opposed to the side of the Royal Palace, which is close to the Little Gellért Hill.

[35] Under his command the engineering captains Pollini and Gorini supervised the work of 200 soldiers and that of many laborers from the capitals and from the Swabian villages around them, to strengthen the weak points of the fortifications, paying them a salary.

[35] Hentzi decreed that the waterworks of Buda, which supplied the castle with water from the Danube, should be fortified with palisades facing north and south, to be defended by his soldiers, and a defensive work in what is now Clark Ádám Place, in which they could take cover.

[37] The Austrian defence force Major General Heinrich Hentzi von Arthurm Infantry Cavalry Artillery Sappers Total: 4764 soldiers, 293 horses, 85 cannons.

(Asbóth) independent reserve division: The total number of the different Hungarian units which participated in the siege of Buda: - I. corps (Major General József Nagysándor): 9465 soldiers, 32 cannons; - II.

[5] After this, Kmety reported to Görgei that it was impossible to take the Waterworks, because the imperial cannon in the castle dominated the road to it, causing heavy losses to the attackers and preventing any chance of success.

[48] During the wait for the siege artillery, Görgei ordered feinting night attacks against the castle, to keep the enemy busy and to divert Hentzi's attention from his true intent.

Many of those that were poorly targeted explode in the air, and the flames pour out of their ripped orbs like squeezed lightning, followed every time by a horrible crack, their fragments whirr with different noises, dispersing in every direction, smashing and crushing whatever stands in their way.

[63] In his council of war that night, he proposed continuing to bombard Pest; but engineering captain Philipp Pollini objected, arguing that it would be better to fire on the Hungarian artillery, in order to try to destroy it.

[66] The 28th, 44th, and 47th battalions advanced undetected right up to the breach, where they were spotted by the surprised defenders, who however resisted fiercely, stopping the Hungarians for a while, with the help of concentrated fire from front and flanks from the Austrian soldiers on the walls and bastions nearby.

[57] The Hungarians who entered the castle faced enemy infantry and artillery units at strategic points, who fired volleys and grapeshot at them; but they continued the assault, overwhelming, killing, or capturing the imperial soldiers.

[66] Then, after the first troops had entered the castle, the 9th Battalion joined them, climbing the ladders near the Vienna Gate, and then manned the captured enemy guns near the 4th rondella, turning them against the retreating imperial soldiers.

[66][68] At 4 am, the Italian soldiers of the Ceccopieri regiment, who were fighting on the western walls of the southern end of the Castle Hill, by the Palace, in the region of the Riding Hall (Lovarda) and the Stables, surrendered.

[68] It was at this critical point that Hentzi, hearing what was happening in Szent György Square, rushed there with two companies of border guards and another two from the Wilhelm regiment, and stood at the head of the defenders trying to repel the Hungarians.

[72] As we showed above, Feldzeugmeister Ludwig von Welden's orders to Hentzi contained nothing about destroying Pest; he gave permission only to bombard the city on the eastern bank of the Danube in exceptional situations, if the civilians behaved towards the castle in an unacceptable manner, which they did not.

When asked why he wanted this, he replied that he knew that if he recovered, Görgei would hang him, remembering that in his letter demanding the surrender of the castle the Hungarian general had threatened to do so if Hentzi bombarded Pest or blew up the Chain Bridge.

Görgei indeed had not forgotten his promise of 4 May, and declared to Lieutenant-Colonel Bódog Bátori Sulcz that he would hang Hentzi the next day if he recovered, saying that the Austrian general did not deserve to be called a hero.

He said that he did not deserve these and did not approve of the greed of many soldiers and officers for rank and decorations, which was not compatible with Prime Minister Szemere's Republican political program, and that by refusing these distinctions he wanted to set an example for his subordinates.

[80] Imperial reports show a constant concern, lasting several weeks, regarding a possible Hungarian attack against Austria that would be helped by revolutionary forces in Vienna and the Austrian provinces.

), before and during the siege of Buda the Hungarian army was actually so numerically inferior compared to the imperial forces gathered around Pozsony and Vienna that the Habsburg commanders' fears were groundless.

It is telling that the very day Buda was captured, Francis Joseph I finalised an agreement by which Tsar Nicholas I of Russia would send 200,000 soldiers to crush the Hungarian Revolution.

[71] The Capture of Buda is regarded as the conclusion of the Hungarian army's victorious Spring Campaign, which resulted in the liberation of almost all Hungary from the Habsburg troops and their Russian, Serbian, Croatian, and Romanian allies.

In the face of these, the numerically and technologically desperately inferior Hungarian army, despite its admirable bearing which earned the respect of the enemy commanders, could only put up a heroic but hopeless resistance before it was defeated and forced to lay down its arms at Nagyszőlős on 13 August 1849 and at Komárom on 2 October 1849.