Examples of "friendly fire," i.e. soldiers inadvertently attacking their comrades, rather than the enemy, are known from the Peloponnesian War (Delium, 424 B.C.: Thucydides 4.96.3; Epipolae, 413 B.C.: Thucydides 7.44). Here is a fictional example from the Trojan War, told by Quintus Smyrnaeus, 11.247-254 (tr. Frederick M. Combellack):
When they were busy with the toil of battle, the restless winds raised a great dust storm. It darkened all the vast sky above, like a fog that reduces visibility to zero. It concealed the ground and destroyed the men's ability to see. But even so, they fought. They recklessly killed anyone they laid their hands on, even if he was a great friend. There was no way to determine in the tumult whether the man who approached was a friend or an enemy. The soldiers felt helpless.
καί ῥ᾽ οἱ μὲν πονέοντο· κόνιν δ᾽ ἀκάμαντες ἀῆται
ὦρσαν ἀπειρεσίην· ἤχλυσε δὲ πᾶσαν ὕπερθεν
ἠέρα θεσπεσίην, ὥς τ᾽ ἀπροτίοπτος ὀμίχλη,
οὐδ᾽ ἄρα φαίνετο γαῖα, βροτῶν δ᾽ ἀμάθυνεν ὀπωπάς·
ἀλλὰ καὶ ὣς μάρναντο· καὶ ἐς χέρας ὅντιν᾽ ἕλοντο
κτεῖνον ἀνηλεγέως, καὶ εἰ μάλα φίλτατος ἦεν·
οὐ γὰρ ἔην φράσσασθαι ἀνὰ κλόνον οὔτ᾽ ἐπιόντα
δήιον οὔτ᾽ ἄρ᾽ ἑταῖρον· ἀμηχανίη δ᾽ ἔχε λαούς.