Titus Livius (Livy), The History of Rome, Book 35
Evan T. Sage, PhD professor of latin and head of the department of classics in the University of Pittsburgh, Ed.

27. Nabis, both gladdened by the victory and filled also with the unquestioning hope that there would no longer be any danger from the sea, wanted to close the land approaches too by suitably-placed guards. [2] Withdrawing one-third of his troops from the siege of Gytheum, he encamped near Pleiae; this place threatens both Leuci and Acriae, where it was evident that the enemy would bring up their army. [3] When he had placed his base there and only a few had tents, but the rest of the throng had huts woven out of reeds and thatched with leaves, which offered nothing but shade, Philopoemen, before he came [4??] in sight of the enemy, determined to attack him unexpectedly with a new kind of warfare. [5] He collected small boats in a secret haven in Argive territory; into them he loaded lightly-equipped soldiers, mostly caetrati,¹ with slings and darts and other kinds of light ordnance. [6] Then, skirting the [p. 77]shore, when he came to a headland near the camp² of the enemy, he landed and travelling over familiar trails by night came to Pleiae and, the sentinels being asleep, like men in no immediate peril, hurled firebrands upon the huts on every side of the camp. Many were consumed by the flames before they knew of the enemy's approach, and those who did know of it were able to bring them no aid. [7] With sword and fire everything was destroyed; a very few escaped from this two-fold destruction to Gytheum and the larger camp. [8] Having thus inflicted a defeat upon the enemy, Philopoemen marched straight to ravage Tripolis in Spartan territory, this being nearest the borders of the Megalopolitae, and having [9??] carried off thence a large number of animals and men departed before the tyrant from Gytheum could send guards over the land. [10] Thence, having mustered the army at Tegea and calling a council at the same place,³ of both Achaeans and allies, at which the leading [11??] men of the Epirotes and Acarnanians were also present, he determined, since on the one hand the courage of his own men was [12??] restored after the shame of the defeat on the sea, and on the other the enemy was terrified, to lead the army against Lacedaemon, thinking that in that way alone the enemy could be drawn away from the siege of Gytheum. He first pitched camp at Caryae in the enemy's country. On that very day Gytheum was captured. [13] Philopoemen, in ignorance of this fact, moved his camp forward to Barnosthenes —this is a mountain ten miles from Lacedaemon. [14] And Nabis, having regained Gytheum, left there with his army in light marching order, and having speedily passed Lacedaemon, occupied what they call the camp of Pyrrhus,⁴ [p. 79]a place that he did not doubt would be attacked by⁵ the Achaeans. There he met the enemy. [15] They were now spread out over a stretch of about five miles, their column being elongated on account of the narrowness of the road; the rearguard was composed of the cavalry and the mass of the auxiliaries, because Philopoemen thought that the tyrant would attack him from the rear with his mercenary troops, in whom he placed most confidence. [16] Two unexpected situations at one time filled him with dismay: first, the fact that the place which he sought had already been occupied; second, that he saw the enemy confronting his van, where, since the way led through rough country, he did not see how the standards could be advanced without a screen of light troops.