Fort Tucson existed to hold a line. Founded by Hugh O'Conor and built between 1775 and 1783, Presidio San Augustin del Tucson protected Spanish communication and trade routes stretching from northern Sonora to southern Alta California. The garrison typically numbered forty to sixty cavalry, mostly Sonorans, supplemented by Pima scouts who had left their traditional tribal structures to serve the Spanish crown. The fort itself was a formidable construction: adobe walls rising from ten to nearly thirty feet in height, surrounded by a water-filled ditch and a palisade of logs. Four bulwarks held cannons at unknown intervals. Two gates, one facing east and one west, controlled access. Across the Santa Cruz River to the northwest lay Indian Town, connected to the presidio by a single bridge. Outside the palisade, soldier and citizen houses stood protected only by the fort's artillery.

The Apaches had reason to attack in force. By 1782, the Spanish had been waging war against Apache bands throughout the Tucson region for years. The garrison had already repelled an attack in 1779, remembered as the First Battle of Tucson. Smaller skirmishes continued through 1780, and Apache raiders regularly struck at wagon trains and unprotected convoys. But something changed in 1782. Rather than the hit-and-run tactics that had characterized earlier conflicts, the Apaches began massing in larger numbers to attack fortified positions. The force of six hundred warriors that descended on Tucson that May Day morning was payback for a recent Spanish campaign that had penetrated deep into Apache territory. This was not a raid. This was an attempt to capture the presidio itself.

The Apache force divided with precision. One column stormed into Indian Town from the north, overwhelming the lightly defended Pima settlement before advancing on the bridge connecting the pueblo to Tucson. A smaller Spanish force held that bridge against over two hundred warriors, their muskets proving decisive against bows and arrows. Meanwhile, the second Apache column rushed the open western gate of Fort Tucson. Captain Allande and four soldiers, positioned on a bridge above the gate, poured cannon and musket fire into the attackers. But the real hero of the western defense was Lieutenant Miguel de Urrea. From the roof of his parapet-topped house, which flanked the Apache approach, Urrea and his native servant held off over one hundred and forty warriors who might otherwise have reinforced the main assault on the fort. Jesuit missionaries watching from within the walls counted around two hundred Apaches fighting on foot, declining to estimate how many more were mounted on horseback.

After two hours, the Apache war chief ordered a retreat. The Spanish confirmed eight Apache dead, though other accounts suggest as many as thirty died in the engagement. Lieutenant Urrea personally killed or wounded at least five attackers from his rooftop position. Captain Allande killed two more. One soldier, Jose Antonio Delgado, spent the entire battle hiding in a tree but provided valuable intelligence afterward: he witnessed Apache warriors carrying three dead and multiple wounded off the field into the surrounding desert, casualties of the cannon fire that had broken the assault. The Spanish lost one trooper and had three wounded. One female civilian was killed by the attackers. The Apaches were known for immediately removing their casualties from the battlefield, making true casualty counts impossible to verify.

The Second Battle of Tucson was a Spanish victory, but not a decisive one. The Apaches returned on December 15 of that same year, raiding livestock in what became the Third Battle of Tucson. That engagement also ended in Spanish favor, with a handful of warriors killed. Throughout the colonial period, Spanish records show that Apache casualties in any single engagement rarely exceeded fifty dead, a testament to the effectiveness of Apache evasion tactics. The May Day attack of 1782 demonstrated both the vulnerability of frontier outposts caught off guard and the remarkable improvisation of defenders like Urrea, whose fortified house became an unplanned bastion. Today, downtown Tucson covers the ground where forty-two lancers, twenty dragoons, and ten Pima scouts held the line against the largest Apache force their captain had ever faced.