First of all, what actually happened?

For some time past there had been tension throughout Catalonia. Earlier in this book I have given some account of the struggle between Communists and Anarchists. By May 1937 things had reached a point at which some kind of violent outbreak could be regarded as inevitable. The immediate cause of friction was the Government’s order to surrender all private weapons, coinciding with the decision to build up a heavily-armed ‘non-political’ police-force from which trade union members were to be excluded. The meaning of this was obvious to everyone; and it was also obvious that the next move would be the taking over of some of the key industries controlled by the CNT. In addition there was a certain amount of resentment among the working classes because of the growing contrast of wealth and poverty and a general vague feeling that the revolution had been sabotaged. Many people were agreeably surprised when there was no rioting on 1 May. On 3 May the Government decided to take over the Telephone Exchange, which had been operated since the beginning of the war mainly by CNT workers; it was alleged that it was badly run and that official calls were being tapped. Salas, the Chief of Police (who may or may not have been exceeding his orders), sent three lorry-loads of armed Assault Guards to seize the building, while the streets outside were cleared by armed police in civilian clothes. At about the same time bands of Assault Guards seized various other buildings in strategic spots. Whatever the real intention may have been, there was a widespread belief that this was the signal for a general attack on the CNT by the Assault Guards and the PSUC (Communists and Socialists). The word flew round the town that the workers’ buildings were being attacked, armed Anarchists appeared on the streets, work ceased, and fighting broke out immediately. That night and the next morning barricades were built all over the town, and there was no break in the fighting until the morning of 6 May. The fighting was, however, mainly defensive on both sides. Buildings were besieged, but, so far as I know, none were stormed, and there was no use of artillery. Roughly speaking, the CNT–FAI–POUM forces held the working-class suburbs, and the armed police-forces and the PSUC held the central and official portion of the town. On 6 May there was an armistice, but fighting soon broke out again, probably because of premature attempts by Assault Guards to disarm CNT workers. Next morning, however, the people began to leave the barricades of their own accord. Up till, roughly, the night of 5 May the CNT had had the better of it, and large numbers of Assault Guards had surrendered. But there was no generally accepted leadership and no fixed plan – indeed, so far as one could judge, no plan at all except a vague determination to resist the Assault Guards. The official leaders of the CNT had joined with those of the UGT in imploring everyone to go back to work; above all, food was running short. In such circumstances nobody was sure enough of the issue to go on fighting. By the afternoon of 7 May conditions were almost normal. That evening six thousand Assault Guards, sent by sea from Valencia, arrived and took control of the town. The Government issued an order for the surrender of all arms except those held by the regular forces, and during the next few days large numbers of arms were seized. The casualties during the fighting were officially given out as four hundred killed and about a thousand wounded. Four hundred killed is possibly an exaggeration, but as there is no way of verifying this we must accept it as accurate.