Early in summer, on the Macedonians and Achaeans rejoining from their winter quarters, Antigonus advanced with his own army and the allies into <a class="linkToPlace" target="_blank" href="/place?placename=Laconia&groupId=662&placeId=1211">Laconia</a>.
His Macedonian forces consisted of ten thousand to form the phalanx, three thousand peltasts, and three hundred horse. He had besides a thousand Agrianians, and a thousand Gauls, while his mercenary force numbered three thousand foot and three hundred horse.
The Achaeans furnished three thousand picked infantry and three hundred horse. There were also a thousand Megalopolitans armed in the Macedonian manner under the command of Cercidas of <a class="linkToPlace" target="_blank" href="/place?placename=Megalopolis&groupId=745&placeId=1360">Megalopolis</a>.
The allies consisted of two thousand Boeotian foot and two hundred horse, a thousand Epirot foot and fifty horse, the same number of Acarnanians, and one thousand six hundred Illyrians under the command of Demetrius of <a class="linkToPlace" target="_blank" href="/place?placename=Pharos&groupId=879&placeId=1586">Pharos</a>.
His total force thus amounted to twenty-eight thousand foot and one thousand two hundred horse.
Cleomenes, who expected the invasion, had occupied the other passes into <a class="linkToPlace" target="_blank" href="/place?placename=Laconia&groupId=662&placeId=1211">Laconia</a>, placing garrisons in them and fortifying them by means of trenches and barricades of trees,
and himself encamped at a place called <a class="linkToPlace" target="_blank" href="/place?placename=Sellasia&groupId=966&placeId=1714">Sellasia</a>, with a force of twenty thousand men, as he conjectured that the invaders would most likely take this route, as in fact they did.
At the actual pass there are two hills, one called <a class="linkToPlace" target="_blank" href="/place?placename=Euas&groupId=583&placeId=1090">Euas</a> and the other Olympus,
the road to <a class="linkToPlace" target="_blank" href="/place?placename=Sparta&groupId=660&placeId=1208">Sparta</a> running between these along the bank of the river <a class="linkToPlace" target="_blank" href="/place?placename=Oenous&groupId=804&placeId=1453">Oenous</a>. Cleomenes, having fortified both of these hills with a trench and palisade, posted on <a class="linkToPlace" target="_blank" href="/place?placename=Euas&groupId=583&placeId=1090">Euas</a> the perioeci and allies under the command of his brother Eucleidas, while he himself held Olympus with the Spartans and mercenaries.
On the low ground beside the river on each side of the road he drew up his cavalry and a certain portion of the mercenaries.
Antigonus on his arrival observed the great natural strength of the position and how Cleomenes had so cleverly occupied the advantageous points with the portions of his force suitable in each case, that his whole formation resembled a charge.
For attack and defence alike nothing was wanting, the position being at one and the same time a fortified camp difficult to approach and a line of battle ready for action.
Walbank Commentary