Titus Livius (Livy), The History of Rome, Book 35
Cyrus Evans, Ed.

27. Nabis, being both elated by this adventure, and entertaining a confident hope that he had not now any danger to apprehend from the sea, resolved to shut up the passages on the land also, by parties stationed in proper posts. [2] With this view, he drew off a third part of his forces from the siege of Gythium, and encamped them at Pleiae, a place which commands both Leucae and Acriae, on the road by which the enemy's army seemed likely to advance. [3] While his quarters were here, and very few of his men had tents, (the generality of them having formed huts of reeds interwoven, and which they covered with leaves of trees, to serve merely as [4??] a shelter,) Philopœmen, before he came within sight, resolved to surprise him by an attack of such a kind as he did not expect. [5] He drew together some small ships in a remote creek, on the coast of the territory of Argos, and embarked on board them a body of light-armed soldiers, mostly targeteers, furnished with slings, javelins, and other light kinds of weapons. [6] He then coasted along the shore, until he came to a promontory near Nabis's post. Here he landed; and made his way, by night, through paths with which he was well acquainted, to Pleiae, and while the sentinels were fast asleep, as being in no immediate apprehension, he set fire to the huts in every part of the camp. [7] Great numbers perished in the flames before they could discover the enemy's arrival, and those who did discover it could give no assistance; so that nearly the whole was destroyed by fire and sword. [8] From both these means of destruction, however, a very small number made their escape, and fled to the principal camp before Gythium. [9] The enemy [p. 1580]having been thus smitten with disaster, Philopœmen forthwith led on his forces to ravage the district of Tripolis, a part of the Lacedaemonian territory, lying [10??] next to the frontiers of the Megalopolitans, and carrying off thence a vast number of men and cattle, withdrew before the tyrant could send a force from Gythium to protect the country. [11] He then collected his whole force at Tegea, to which place he summoned a council of the Achaeans and their allies; at which were present, also, deputies from the Epirots and Acarnanians. [12] Here it was resolved, that as the minds of his men were now sufficiently recovered from the shame of the disgrace suffered at sea, and those of the enemy dispirited, he should march directly to Lacedaemon; for he considered that by this measure alone could the enemy be drawn off from the siege of Gythium. [13] On entering the enemy's country, he encamped the first day at Caryae; and, on that very day, Gythium was taken. Ignorant of that event, Philopœmen advanced to the Barbosthenes, a mountain ten miles from Lacedaemon. [14] On the other side, Nabis, after taking possession of Gythium, set out, at the head of a body of light troops, marched hastily by Lacedaemon, and seized on a place called the Camp of Pyrrhus, which post he did not doubt that the Achaeans intended to occupy. From thence he proceeded to meet the enemy. [15] From the length of their train in consequence of the narrowness of the road, they spread over a space of almost five miles. The line was closed by the cavalry and the greatest part of the auxiliaries, because Philopœmen expected that the tyrant would attack him in the rear with his mercenary troops, in whom he placed his principal confidence. [16] Two unforeseen circumstances at once filled him with uneasiness: one, the post at which he aimed being pre-occupied; the other, the enemy having met him in front, where, as the road lay through very uneven ground, he did not see how the battalions could advance without the support of the light troops.