The first large battle occurred on May 9-10-11-12th outside of Guaymas, between Ojeda's Federals and Obregon's Constitutionalists, at a place called Santa Rosa. The Federal advance north consisted of about twelve hundred men and eighteen pieces of artillery. They were opposed by about four thousand men under Obregon, without artillery. Eight hundred Federals were killed and all their artillery captured. The Constitutionalists lost two hundred and fifty men killed and wounded. Comparatively few Federals returned to Guaymas. Each side killed all the wounded that they found, and also all captives who refused to enlist in the captor's force. This success was not followed up and Guaymas remained in the hands of the Federals. The artillery captured by the Constitutionalists had had the breech blocks removed to render them unserviceable; new ones, however, were made in the shops at Cananca by a German mechanician named Klaus. In the summer, Urbina captured the city of Durango, annihilating the Federals. The city was given over to loot and the greatest excesses were indulged in by the victors. Arson, rape, and the robbing of banks, stores, and private houses were indiscriminately carried on. Horses were stabled in the parlors of the homes of the prosperous citizens, and many non-combatants were killed by the soldiers before order was restored. At this time the only points held by the Federals on the boundary between the United States and Mexico were Juarez, in Chihuahua, and Nuevo Laredo, in Tamaulipas. The railroads south of these points were also in the physical possession of the Federals but subject to continual interruption at the hands of the Constitutionalists. Venustiano Carranza had established headquarters at Ciudad Porfirio Diaz (Piedras Negras) across the Rio Grande from Eagle Pass, Tex. He started on a trip, during the late summer, through the northern provinces to confer with the leaders of the Constitutionalist movement in order to bring about better coordination of effort on their part. He went through the States of Coahuila, Durango, Chihuahua, and Sonora and established a new headquarters in Sonora. Since then the efforts of the Constitutionalists have been much better coordinated, with the result that they have had much better success.