The Klerouchoi Phalangitai are Hellenes or Hellenized soldiers who receive a 'kleros,' or land allotment, in return for military service, and form a large portion of the phalanx of the eastern Diadochoi.
Can Form Phalanx
The Klerouchoi Phalangitai form the backbone of the Successor armies of Aigyptos and Asia, along with the less numerous Pezhetairoi. These men are given a plot of land or kleros, maybe some slaves and a tax reduction and in return they serve in the phalanx when called upon to war by their Basileus. They are citizens just as the Pezhetairoi, but they are citizens with-strings-attached, as they are required to fight when called upon or otherwise their livelihood might be taken away from them.
Even though the phalanx is a Hellenic soldier formation, some Thraikes, Keltoi, Ioudaioi and other subjects were also given Klerouchos status to increase the number of Phalangitai available, but the main bulk of the Klerouchoi Phalangitai are still Hellenes. Each soldier is armed with the sarissa and wears a linen or leather cuirass, a Thracian helm, and a Makedonian pelte provided by the Basileus. In battle they are best deployed in a defensive posture, or in a slow but steady advance towards the enemy, grinding down their opponents' numbers through attrition, or to pin enemy formations so they can be flanked by other units.
The wars which followed the breakup of Megas Alexandros' empire drained the Makedonian armies of many of their Makedones. For the western Diadochoi, levies from populations could take place directly, but the eastern Diadochoi depended on their dwindling standing armies or on new mercenary recruits. They needed a renewable source of Hellenic recruits if they were to keep power and retain their military strength. As the pike-phalanx was the backbone of their armies, they needed Hellenes to fill its ranks. While mercenaries could temporarily fulfill such a need, their loyalty was never assured, while their demands for pay always were.
The answer was the establishment of Hellenic military-settlements throughout the Successor states, where a soldier was given a plot of land and reduced taxes. Sometimes they were given some slaves too, to work their alloted land, freeing up more time for the Klerouchos soldier to be on campaign. Arming the native population (Aigyptioi in the Ptolemaic kingdom, Syriakoi and Babylonioi in the Seleukid Empire), was less appealing, as that would have laid the Makedonian dynasties open for native revolts in their respective heartlands. In Aigyptos most Klerouchoi were settled in the Fayum depression, but many others were settled further to the south, though in smaller numbers.
Klerouchoi were also settled by the Ptolemaioi in settlements in Asia, Kypros, and Koile Syria, but nearly all Hellenic, Klerouchoi Phalangitai were settled in Aigyptos, and primarily in the Arsinoite and Herakleopolite nomes, in or near the Fayum. In the Arche Seleukeia these settlements, called Katoikiai, were established in western Asia around Sardis, throughout Syria and Mesopotamia, and as far away as Baktria and Paropamisadai. The Klerouchoi population in Aigyptos eventually deteriorated, and lost much of its martial character after the arrival of the Romans, while the Katoikiai in Seleukid regions, especially those in western Asia, passed into the hands of the Pergamenes first, then Pontos, and finally the Romaioi.