During the siege of Montevideo, the newly-freed slaves, who formed a contingent 5,000 strong, and the community of foreign exiles and expatriates, were mostly responsible for the defence of the city.
Their lances, longer than normal length, their dark black [nerissimi] faces, their robust limbs used to permanent and demanding work, their perfect discipline".
"A moor [moro] of vast proportions who had followed [Garibaldi] from America, in a black cloak with a lance garnished with a red pennant" was the description of the Swiss volunteer Von Hofstetter.
In one specific episode, during battle with soldiers of the Bourbon Kingdom of the Two Sicilies at Velletri, Aguyar saved Garibaldi when the commander was thrown of his horse and was in concrete danger of being captured.
Off the battlefield, Aguyar is mentioned as offering his saddle as a pillow for Garibaldi to sleep on during breaks in marching, and improvising an awning to protect him from the sun.
With the French forces breaking into Rome on 30 June 1849, Andrea Aguyar - appointed a Lieutenant by Garibaldi in recognition of his abilities - was mortally wounded when hit by a shell near the Church of Santa Maria in Trastevere.