On 20 July 1928, a coup attempt is planned by the "Liga de Paris", Major Sarmento Beires, and military leaders of the Portuguese mainland interior, which are supported by various syndicalists (namely railroad syndicalist workers). But the negotiations are hard and the government's forces learn about the plot and preemptively bomb São Jorge Castle, where the rebels are located. This causes the rebel forces within Castelo de São Jorge to start the plot, hours before the provincial rebel forces arrive in Lisbon. The rebel forces in Lisbon surrender on the morning of 21 July 1928 and the forces outside the capital at 22 July the latest. About 1100 military members and 200 civilians are imprisoned, many of which are later exiled.