Canto 3 -
Araṇya-kāṇḍa
Chapter 45: Sītā Chastises Lakṣmaṇa
Text 3.45.16

न च तस्य स्वरो व्यक्तं मायया केनचित्कृतः।
गन्धर्वनगरप्रख्या माया सा तस्य रक्षसः॥

na ca tasya svaro vyaktaṁ māyayā kenacit kṛtaḥ
gandharva-nagara-prakhyā māyā sā tasya rakṣasaḥ

na ca = it is not; tasya = Rāma’s; svaraḥ = voice; vyaktam = clearly; māyayā = through his diverse powers; kenacit = by someone [else]; kṛtaḥ = it has been produced; gandharva-nagara-prakhyā = is like a city of the gandharvas; māyā = magic; = the; tasya = of that; rakṣasaḥ = rākṣasa.

Clearly, it is not Rāma’s voice. It has been produced by someone [else] through his diverse powers. The magic of that rākṣasa is like a city of the gandharvas.

In the second half of the verse, Lakṣmaṇa states that actually the magic was that of Mārīca who had [earlier] assumed the form of a deer.

“A city of the gandharvas” refers to the palace, forest and so on imagined to be formed on clouds and so on. It is sometimes seen and it deludes one [to think that he is seeing the palace, forest and so on]. Similarly, the rākṣasa Mārīca had a certain astonishing potency to provide an even greater delusion by which Sītā-devī became bewildered.1 Some state—gandharva-nagaraṁ proktam indrajālaṁ manīṣibhiḥ: “The intelligent declare ‘the city of the gandharvas’ to be magic.”2

1 Rāmāyaṇa-bhūṣaṇa: gandharva-nagaraṁ nāma meghādāv āropitaṁ prāsāda-vanādikam. tat kadācid dṛśyate tad yathā vyāmoha-janakaṁ tathā citra-vastu-rūpā para-vyāmoha-janikā kācic chaktir māyā sā tasya rakṣasaḥ mārīcasyāsti yayā muhyasīti 

2 Magic meaning the magic of a professional magician.