Valmiki Ramayana 5.2.33

अनेन रूपेण मया न शक्या रक्षसां पुरी ।प्रवेष्टुं राक्षसैर्गुप्ता क्रूरैर्बलसमन्वितैः॥

anena rūpeṇa mayā na śakyā rakṣasāṃ purī |praveṣṭuṃ rākṣasairguptā krūrairbalasamanvitaiḥ ||

Our plain-language meaning of this verse is waiting for scholar review.