On 2 September, Flores suggested an immediate attack on Uruguaiana, an option rejected by Porto Alegre and Joaquim Marques Lisboa (then-Viscount and later Marquis of Tamandaré), the commander-in-chief of the Brazilian Navy.

[citation needed] The allied troops united under Emperor Pedro II of Brazil, the Count d'Eu, and President Mitre in the camp of Concordia, in the Argentine province of Entre Ríos.

[1]: 39  Since his arrival in Uruguaiana, Mitre had claimed the position of commander-in-chief of all allied forces participating in the siege—a precedence which Porto Alegre vehemently refused to recognize.

The Brazilian monarch settled the dispute when, at his suggestion, the allied army was divided into three forces, one led by Porto Alegre and the other two by Mitre and Flores.

[4] A call for Uruguaiana to surrender was ignored on 4 Sept.[1]: 40  On 11 September, emperor Pedro II arrived at the scene of the siege, where were the presidents of Argentina, Bartolomé Mitre and Uruguay, Venancio Flores, and several military leaders, such as Admiral Tamandaré.