Visible from everywhere in town, at 130m (430 ft.), the rusty-colored giant rock is Arica's most distinguishing feature. Geologically, it marks the end of the coastal range that runs the entire length of the country. Chilean troops captured the hill on June 7, 1880, in a dawn attack on a surrounded Peruvian garrison that had refused to surrender. Cannons and other pieces of artillery mark the site, along with a large statue of Christ, adorned with the coats of arms of both nations, asking for reconciliation. You can walk to the summit from near the end of Colón, or drive or take a taxi. From there, you'll be able to see all the way to the border, taking in the panorama of the city, port, and Azapa Valley, and it's certainly worth a trip back to take in the view at night.
The army owns and operates the Morro's commemorative museum that explains the siege and combat in great detail, along with displaying uniforms and weapons of the war. Though former dictator Augusto Pinochet himself placed several plaques there that remain on display, it's not offensively nationalistic, but it also doesn't make much of an effort to explain the war itself.