The Battle of Madrid in November 1936 saw the most intense fighting in and around the city when the Nationalists made their most determined attempt to take the Republican capital.

Giral agreed to arm the trade unionists to defend the Republic and had 60,000 rifles delivered to the CNT and UGT headquarters although only 5,000 were in working order.

The fighting was chaotic, and on several occasions, some soldiers in the barracks indicated their willingness to surrender, only for other troops to keep firing at the attackers, which killed those who had broken cover to take them prisoner.

Eventually, the barracks fell when the Guardias de Asalto brought up a 75 mm field gun to bombard the complex and its gate was opened by a sapper sergeant sympathetic to the Republicans.

However, resistance to the coup by Republicans meant that Francisco Franco and his allies instead had to conquer the country by military force if they wanted to seize power.

Franco's veteran colonial troops, or regulares, under General Juan Yagüe, along with air cover supplied by Nazi Germany, routed the Republican militias in their path.

The term "fifth column" became a synonym for spies or traitors for Republicans, and paranoia led to massacre of Nationalist prisoners in Madrid during the ensuing battle.

The Republicans had a geographical advantage in defending Madrid: the River Manzanares separated the Nationalists from the city centre and was a formidable physical obstacle.

Colonel Romero commanded Republican forces there and effectively repelled attempts to cross it and to gain access to Madrid's city centre.

Some regulares eventually broke through and made an initial crossing over the Manzanares towards the Modelo Prison, the target of the offensive, but the attack stalled at the western fringe of the city.

The foreign troops, while actually a mixture of volunteers from Germany, France, Britain and various other nations, including Winston Churchill's nephew, Esmond Romilly, were greeted with cries of vivan los rusos ("long live the Russians") by madrileños since they had been mistaken for Soviet infantry.

The colonial Moroccan troops were pinned down in house-to-house fighting (in which they had little previous experience since their greatest strength was in open-country warfare) and took heavy casualties at the hands of militiamen who knew the urban terrain very well.

In the evening of 9 November, General Kléber launched an assault of the XI International Brigade on the Nationalist positions in the Casa de Campo, which lasted for the whole night and part of the next morning.

At the end of the fight, the Nationalist troops had been forced to retreat and abandoned all hopes of a direct assault on Madrid through the Casa de Campo, while the XIth Brigade had lost a third of its men.

Meanwhile, Republican troops counterattacked all along the front in Madrid, on 9, 10 and 17 November, driving the Nationalists back at some places, but taking heavy casualties in the process.

Colonel Romero had disagreements with anarchists, asked for the dismissal of Ricardo Sanz and proposed the dissolution of the Durruti Column and the distribution of their men among other units.

[16] On the 12th, the newly arrived XII International Brigade, under General Mate "Lukacs" Zalka with German, Scandinavian, French, Belgian and Italian troops, launched an attack on Nationalist positions on the Cerro de los Ángeles hill, south of the city, to prevent the cutting off of the Valencia road.

[18] Despite fierce counterattacks by the XI International Brigade and Spanish Republican units, the Nationalists kept their toehold in the University City and, by the end of the battle, were in possession of three quarters of the complex.

Having failed to take Madrid by assault, Franco ordered the aerial bombardment of the city's residential areas except for the upper-class Salamanca district, which was assumed to contain many Nationalist supporters,[19] with the intention of terrifying the civilian population into surrender.

Arguably, that tactic by Franco was counter-productive, as the Republican population in Madrid was not cowed into surrender, and the aerial bombardment of civilians, one of the first in the history of warfare, was heavily criticised by foreign journalists such as Ernest Hemingway.

From early 1937 onward, fighter resistance and Republican pilots' experience had also grown too strong for further bombing to occur during daylight, which further limited its effectiveness.

The casualties inflicted in the Battle of Madrid were never accurately counted, but the British historian Hugh Thomas estimated that they were a total about 10,000 for both sides and the civilian population.

In addition, two other battles were fought further afield as part of the Nationalist campaign to take the capital: in March, at Guadalajara and at the end of December at Teruel, both north east of Madrid.

[22] In May, Republican forces under the Polish communist officer Karol Świerczewski, tried to break out of Madrid in an armoured assault but were beaten back.

At the very end of the year, the Republican commander of the IV Corps at the time, Cipriano Mera intercepted Nationalist plans for a fresh assault on Madrid from the direction of Zaragoza.

Rojo's offensive put paid to Franco's proposed assault on Madrid, but led to one of the bloodiest battles of the war, with over 100,000 casualties on both sides.

On 5 March, Casado's men arrested communist officers in Madrid, stripped them of their powers, deposed Negrín and established the National Defence Council (Consejo Nacional de Defensa) to negotiate a peace deal with Franco.

On 26 March, Franco ordered a general advance into Madrid, and on the 27th, the Republican front collapsed, many of whose troops surrendered or simply threw away their weapons and started for home.

The besieged capital of Spain, with the enemy so close, yet unable to take the city for years on end, became the subject of songs, such as Los Emboscados – a version of Si me quieres escribir,[27] and poems like this one by renowned poet Rafael Alberti, Madrid, corazón de España, which begins thus: The Siege of Madrid, particularly the Battle of Brunete, is referenced in Ernest Hemingway's 1940 novel For Whom The Bell Tolls multiple times.

The latter poem, first published in the Warsaw weekly Czarno na Białem, described graffiti written by dying Republican soldiers as a beacon of hope against fascism.