The battle took place at the Inti Urqu (Intiorko) hill plateau, a few miles north of the Peruvian city of Tacna.

The Chilean government believed that with the capture of Tarapacá, Peru would sign a truce, allowing Chile to keep the recently gained territory as war compensation.

This was determinant for the deposition of the President of Peru, Mariano Ignacio Prado, and his Bolivian counterpart, Hilarión Daza.

Also, the loss of the Tarapacá Department stopped the earnings of the saltpeter trade, making the war financial weight heavier for the Allies.

[10] By the time of the battle the sanitary conditions in the city were poor with infectious diseases being widespread among both soldiers and the civilian population.

[10] Civilians and soldiers alike died of infectious diseases, hospitals were underfunded, and overall the management of the military effort poor.

The Chilean High Command planned a landing at Ilo and Pacocha to scout the country and to gain knowledge of the Allies status.

By the time of these events, Gen. Erasmo Escala resigned his commission as Commander in Chief due to constant arguments with War Minister Rafael Sotomayor.

By the end of the month, the Peruvian stronghold of Los Angeles Hill,[12] -a position considered unbreakable by the Allies- fell to Baquedano.

However, the Peruvian corvette Unión broke through the blockade on Arica, delivering supplies, medicines, and shoes to the port garrison.

The Chilean President Aníbal Pinto appointed the former Lieutenant of the National Guard José Francisco Vergara as the new War Minister in Campaign.

Montero wanted to wait for the Chileans at Tacna, but Col. Eliodoro Camacho supported the idea to march and ambush them at the Sama river valley, easing the communications with Arequipa.

On the night of 25 May, Campero's troops tried to ambush the Chileans at Quebrada Honda, but the darkness and the mist prevented the Allies from doing so, forcing their return to Tacna for defense preparations.

[9] The Intiorko plateau is an arid and soft-sloped terrain located a few miles north from Tacna, becoming an excellent shooting ground.

The flanks are protected by the Sama-Tacna road from the east, and to the west by an almost impossible to walk terrain, where no artillery could ever been placed, and a harsh field for infantry or cavalry movement.

On the other hand, Col. Velasquez had the idea to exploit the lack of depth in the allied lines, and to engage the whole front in a simultaneous charge.

The Chilean army presented at Tacna a total of sixteen battalions, three cavalry regiments and thirty-seven cannons.

[21] After a bitter struggle, the Chileans drove back the Viedma and Victoria battalions,[22] but couldn't break the allied left completely.

However, the charge forced the allied advance to stop, which gave Amengual and Barceló precious time to rally and to resupply.

On the far left, Amengual's men and the “Artillería de Marina” Regiment caught the Bolivians in a heavy cross fire, and after intense fighting, tore them to pieces.

The rest of Amunátegui's and Barceló's divisions regained the terrain previously lost, and finally broke the allied center.

The Zapadores and Lautaro regiments advanced frontally over Montero, while the Cazadores del Desierto Battalion maneuvered to outflank from the far right.

The 2nd Line Regiment banner lost at the battle of Tarapacá was found on a church in Tacna by Ruperto Marchant Pereira.

Second, the Chilean government changed the objective of the conflict, because it became clear that the war would end only with the complete surrender of Peru.