This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
堹 combines 土 (earth) with 重 (heavy). The exact historical development is uncertain, and the character is rare in modern Japanese.
The left side is earth 土 and the right side is heavy 重. Picture heavy earth piled up, but since the meaning is unclear, treat this as a visual reminder only.
For チョウ, imagine a heavy earth mound shaped like a long chou (invented name) stretching across the field: Chou -> チョウ.