An interesting observation making the rounds of various lists and emails ... check out Caesar, Gallic War 5.44:

Erant in ea legione fortissimi viri, centuriones, qui primis ordinibus appropinquarent, Titus Pullo et Lucius Vorenus. Hi perpetuas inter se controversias habebant, quinam anteferretur, omnibusque annis de locis summis simultatibus contendebant. Ex his Pullo, cum acerrime ad munitiones pugnaretur, "Quid dubitas," inquit, " Vorene? aut quem locum tuae probandae virtutis exspectas ? hic dies de nostris controversiis iudicabit." Haec cum dixisset, procedit extra munitiones quaque pars hostium confertissima est visa irrumpit. Ne Vorenus quidem tum sese vallo continet, sed omnium veritus existimationem subsequitur. Mediocri spatio relicto Pullo pilum in hostes immittit atque unum ex multitudine procurrentem traicit; quo percusso et exanimato hunc scutis protegunt, in hostem tela universi coniciunt neque dant regrediendi facultatem. Transfigitur scutum Pulloni et verutum in balteo defigitur. Avertit hic casus vaginam et gladium educere conanti dextram moratur manum, impeditumque hostes circumsistunt. Succurrit inimicus illi Vorenus et laboranti subvenit. Ad hunc se confestim a Pullone omnis multitudo convertit: illum veruto arbitrantur occisum. Gladio comminus rem gerit Vorenus atque uno interfecto reliquos paulum propellit; dum cupidius instat, in locum deiectus inferiorem concidit. Huic rursus circumvento fert subsidium Pullo, atque ambo incolumes compluribus interfectis summa cum laude sese intra munitiones recipiunt. Sic fortuna in contentione et certamine utrumque versavit, ut alter alteri inimicus auxilio salutique esset, neque diiudicari posset, uter utri virtute anteferendus videretur.

... via the Latin Library

In that legion there were two very brave men, centurions, who were now approaching the first ranks, T. Pulfio, and L. Varenus. These used to have continual disputes between them which of them should be preferred, and every year used to contend for promotion with the utmost animosity. When the fight was going on most vigorously before the fortifications, Pulfio, one of them, says, "Why do you hesitate, Varenus? or what [better] opportunity of signalizing your valor do you seek? This very day shall decide our disputes." When he had uttered these words, he proceeds beyond the fortifications, and rushes on that part of the enemy which appeared the thickest. Nor does Varenus remain within the rampart, but respecting the high opinion of all, follows close after. Then, when an inconsiderable space intervened, Pulfio throws his javelin at the enemy, and pierces one of the multitude who was running up, and while the latter was wounded and slain, the enemy cover him with their shields, and all throw their weapons at the other and afford him no opportunity of retreating. The shield of Pulfio is pierced and a javelin is fastened in his belt. This circumstance turns aside his scabbard and obstructs his right hand when attempting to draw his sword: the enemy crowd around him when [thus] embarrassed. His rival runs up to him and succors him in this emergency. Immediately the whole host turn from Pulfio to him, supposing the other to be pierced through by the javelin. Varenus rushes on briskly with his sword and carries on the combat hand to hand, and having slain one man, for a short time drove back the rest: while he urges on too eagerly, slipping into a hollow, he fell. To him, in his turn, when surrounded, Pulfio brings relief; and both having slain a great number, retreat into the fortifications amid the highest applause. Fortune so dealt with both in this rivalry and conflict, that the one competitor was a succor and a safeguard to the other, nor could it be determined which of the two appeared worthy of being preferred to the other.

... via Perseus

Obviously we've got a variant reading in the translation (the same variant is at the Internet Classics Library version), but the description seems to fit ...