Caspian sits next to 4 phonetic neighbors — Casper, Cassian, and Cassius are the closest matches by sound. Most share Caspian's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"of the Caspian Sea"
"beam of light"
"born on Sunday"
"steadfast defender"
"protector of mankind"
"arrow maker"
"mill worker, grain grinder"
"wealth, fortune"
"steadfast, firm"
"sun, lord"
"little fawn"
"whole, universal, powerful"
"one who carries loads, carrier"
"Yahweh is my flame"
"great, venerable, majestic"
"dweller near the ridge"
"dragon"
"rest (via Rocco)"
"fair warrior, white hero"
"from the island of Rhodes"
Similar sound: These names share phonetic patterns with Caspian — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin/Geographic origins, giving them the same cultural heritage as Caspian.
Rhythm: Caspian is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.