Passage 7.16.2
Μόμμιος μὲν δὴ τῶν τε ἐξ Ἰταλίας τινὰς καὶ τὰ ἐπικουρικὰ ἀπωτέρω δύο τε καὶ δέκα ἔταξε σταδίοις, πρὸ τοῦ παντὸς εἶναι στρατεύματος φυλακήν· Ἀχαιοὶ δέ, ἐχόντων ἀφυλακτότερον ὑπὸ φρονήματος τῶν Ῥωμαίων, ἐπιτίθενται τοῖς ἐπὶ φυλακῆς αὐτοῖς τῆς πρώτης, καὶ τοὺς μὲν φονεύουσι, πλείονας δὲ ἔτι ἐς τὸ στρατόπεδον κατεῖρξαν, καὶ ἀσπίδας ὅσον τε πεντακοσίας εἷλον. ἀπὸ τούτου δὲ τοῦ ἔργου καὶ ἐπήρθησαν οἱ Ἀχαιοὶ ποιήσασθαι τὴν ἔξοδον πρότερον πρὶν ἢ Ῥωμαίους ἄρχειν μάχης·
Mummius had placed some of his Italian troops as well as his auxiliary forces twelve stades further forward, in front of the whole army, as a guard. The Achaeans, observing that these sentinels were carelessly posted due to Roman arrogance, attacked their forward guard, killed some, and drove the greater part back into the Roman camp, capturing as many as five hundred shields. Encouraged by this success, the Achaeans were emboldened to sally forth first, before the Romans could initiate the battle.