The Trophimoi were children of non-Spartiatae - Perioeci or foreigners - who underwent Spartan education

Agoge

The agōgē was the rigorous education and training regimen mandated for all male Spartan citizens, except for the firstborn son in the ruling houses, Eurypontid and Agiad. The training involved learning stealth, cultivating loyalty to one's group, military training The agōgē (Greek: ἀγωγή in Attic...

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The trophimoi are temporarily adopted by a Spartan oikos. The trophimoi sons of Perioeci, represent, like the neodamodes

Neodamodes

The Neodamodes were Helots freed after passing a time of service as hoplites in the Spartan Army.The date of their first apparition is uncertain. Thucydides does not explain the origin of this special category. Jean Ducat, in his book Les Hoplites , concludes that their statute "was largely...

 and the nothoi (natural sons of slaves and citizens), an intermediate class at Sparta. They could rise to the status of citizens. According to Plutarch

Plutarch

Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

, Agis IV

Agis IV

Agis IV , the elder son of Eudamidas II, was the 24th king of the Eurypontid dynasty of Sparta. Posterity has reckoned him an idealistic but impractical monarch.-Succession:...

 intended by this mean to strengthen the citizenry, that had become too meagre for Sparta's wartime necessities.

The foreign trophimoi normally left Sparta to return to their native towns, where they increased Sparta's influence. Thus, on the invitation of Agesilaus II

Agesilaus II

Agesilaus II, or Agesilaos II was a king of Sparta, of the Eurypontid dynasty, ruling from approximately 400 BC to 360 BC, during most of which time he was, in Plutarch's words, "as good as thought commander and king of all Greece," and was for the whole of it greatly identified with his...

, Xenophon

Xenophon

Xenophon , son of Gryllus, of the deme Erchia of Athens, also known as Xenophon of Athens, was a Greek historian, soldier, mercenary, philosopher and a contemporary and admirer of Socrates...

 had raised his own sons at Sparta. However, some trophomoi preferred to remain, and fought in the civic army. This was the case, for example, of the army that Agesipolis I

Agesipolis I

Agesipolis I was the twenty-first of the kings of the Agiad dynasty in ancient Sparta.Agesipolis succeeded his father Pausanias, while still a minor, in 394 BC, and reigned fourteen years. Upon the death of Pausanias, Agesipolis and his brother, Cleombrotus I, were both placed under the...

 sent to besiege Phlius

Phlius

Phlius was a Greek city in the northwestern Argolid, in the Peloponnese, said to be named after the Greek hero, Phlias. Although geographically close to Argos, the city became a Spartan ally and a member of the Peloponnesian League....

 in 381 BC

381 BC

Year 381 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Camillus, Albinus, Albinus, Medullinus, Flavus and Ambustus...

:

There followed with him also many of the Perioeci as volunteers, men of the better class, and aliens who belonged to the so-called foster-children [i.e. Trophimoi] of Sparta, and sons of the Spartiatae by Helot women, exceedingly finelooking men, not without experience of the good gifts of the state.

(Xénophon Hellenica

Hellenica (Xenophon)

Hellenica simply means writings on Greek— Hellenic— subjects. Several histories of fourth-century Greece, written in the mold of Thucydides or straying from it, have borne the conventional Latin title Hellenica...

, V. 3)