Castro sits next to 3 phonetic neighbors — Casto, Castor, and Costero are the closest matches by sound. Most share Castro's Spanish-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"castle, fortress"
"unconditional, divine love"
"wise protection"
"devoted to Demeter, of the earth goddess"
"heaven, sky"
"from Magdala"
"God will strengthen, God strengthens"
"one with beautiful eyes"
"ripe grain, harvest"
"topographic surname from a place in England"
Similar sound: These names share phonetic patterns with Castro — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Latin origins, giving them the same cultural heritage as Castro.
Rhythm: Castro is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.