Left-side 阝 is the mound radical 阜 — earthworks, hills, and barriers. A 限 originally meant a hill that blocks passage, hence to limit. Same radical groups it with 防 (defend), 阻 (obstruct), 险 (steep). Distinct from right-side 阝 (city, from 邑).
艮 supplies the sound — gèn → xiàn — and also reinforces the meaning, since 艮 in the trigram system stands for mountain and stopping. Same phonetic family: 跟 (gēn, heel), 根 (gēn, root), 很 (hěn, very), 恨 (hèn, hate).
