"[O]n 22 January [1810], some 60,000 French troops were now concentrated in the Guadalquivir valley. The only Spanish troops left in the area were 8,000 survivors of the fighting around La Carolina, who had reformed around Jaen, and Albuquerque's army [of 8,000 men], which had been ordered to move towards Seville once it became clear that the French were attacking in force. Joseph decided to split his army once again, sending Sebastiani south with 10,000 men to deal with the forces at Jaen, while the main French army advanced on Seville.
On 23 January Sebastiani caught up with Areizaga at Jaen, and dispersed the remnants of his army almost without a fight. Two days later Sebastiani was ordered south to conquer Granada, winning a small battle at Alcada la Real on 28 January and taking possession of the city.
Joseph's main force met with little more resistance. Cordova surrendered on 24 January. The French then made a mistake which would cost them dearly over the next two years. At this point both Seville and Cadiz were open to attack, and both cities could easily have been seized by the French, but Joseph was so obsessed with Seville that he entirely ignored Cadiz. While the French moved on Seville, Albuquerque realised that the situation there was hopeless, and made for Cadiz. By the time the French reached the port city its defences were secure, and despite a two year long siege, the city would never fall to the French. Instead the siege lines outside Cadiz would consume a large part of the French army in Andalusia.
Seville itself fell without a fight. The city had begun a descent into chaos on 18 January when news of Victor's advance arrived. The Junta fled on 23 January and was replaced by a Revolutionary Government, dominated by men out of favour with the Central Junta (although not without merit in their own rights, including amongst them the Marquis de La Romana and Francisco Saavedra, the original head of the Junta of Seville in 1808, and led by Francisco Palafox). When this new Junta realised how weak its defences were, its members also fled (28 January). Without leaders the mob remained defiant but unorganised. When the first French troops appeared on 29 January they were fired at, but on 31 January the corporation of Seville surrendered the city without a fight and on 1 February Joseph entered the city. Somewhat ironically their experience of the Junta and of mob rule convinced many citizens of Seville to make their peace with the French.
Only now did the French realise that Spanish troops were heading for Cadiz. Victor was ordered to march for Cadiz, but he arrived two days too late, on 5 February. Cadiz was securely held, and would become a valuable base for the British and Spanish."
The Spanish Ulcer, A History of the Peninsular War
David Gates
London: Pimlico, 2002
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In greater detail ….
History of the Peninsular War
Vol. 3. – September 1809 to December 1810 – Ocaņa, Cadiz, Bussaco, Torres, Vedras
Charles Oman
Oxford: University Press, 1908
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ponders nirvana.