Indaprasthanagara อินทปรัษฐ์นคร
Ancient settlement
Country	Thailand
Province	Chai Nat province
Re-founded	757 CE

Indapraṣṭhanagara (Thai: อินทปรัษฐ์นคร) is an ancient toponym attested in several Thai textual traditions, including the Ayutthaya Testimonies,^[2]: 5–6 the Chronicle of the Padumasūriyavaṃśa^[3] the Legend of Nakhon Si Thammarat [th],^[4]: 37 the Lan Na Yonok Chronicle [th],^[5]: 166 and the Laotian Phra That Phanom Chronicle.^[6] These sources collectively place the city's historical memory between approximately the early 8th century^[a] and the early 13th century CE,^[b] after which Indaprasthanagara disappears from the record following the rise of the Sukhothai and Ayutthaya kingdoms. Although earlier Thai scholarship long equated Indapraṣṭhanagara with the Angkorian Yaśodharapura,^{[3]: 1, 8–9 [6]} closer chronological and contextual analysis suggests that this identification is problematic, as the existence of Indapraṣṭhanagara predates the establishment of Yaśodharapura by approximately two centuries.^[c]

The earliest narrative associated with Indapraṣṭhanagara situates its foundation in the 8th century CE,^[a] during the late Dvaravati period, a time of political fragmentation in the Menam basin.^[11]: 60 Later traditions associate the city with the Padumasūriyavaṃśa lineage^{[3]: 5 [2]: 5–6, 15–6} and with rulers bearing the regnal name Sri Dharmasokaraja I, whose political activities linked central mainland regions with the upper Malay Peninsula.^{[4]: 37–41} These accounts indicate that Indapraṣṭhanagara functioned as a regional polity of considerable importance prior to the consolidation of Angkorian power and the emergence of Sukhothai.

The reinterpretations founded that Indapraṣṭhanagara was not at Angkor but in the Phraek Si Racha historical region, east of Sankhaburi, as stated in the Ayutthaya Testimonies.^[2]: 5–6 This reassessment has significant implications for understanding dynastic relationships, inter-polity conflicts, and alliances among Sukhothai, Lavo, Angkor, and related polities in the 11th–12th centuries, as well as for re-evaluating traditional narratives preserved in later Thai chronicles.

The earliest reference to Indapraṣṭhanagara appears in the Chronicle of Padumasūriyavaṃśa,^[3]: 5 dated the establishment of Indapraṣṭhanagara to the early 8th century CE.^[a] According to this text, the infant prince Ketumāla and his mother were expelled by his father, Gomerāja, ruler of Pranagara Khemarājadhānī (พระนครเขมราชธานี).^[3]: 2 At the age of three, Ketumāla and his mother established a new settlement on the forested frontier of Pranagara Khemarājadhānī, near the Dong Phaya Fai mountain range, and named it "Indapraṣṭhanagara". Ketumāla was later formally enthroned as a local ruler by his father, resulting from his repeated refusals to return to the capital.^[3]: 4–5

The chronicle further relates that Ketumāla adopted Padumasūriyavaṃśa, who founded another settlement in an accretion area, likewise named "Indapraṣṭhanagara", from which he ruled after his father's death.^[3]: 4–5 While the chronicle does not provide explicit dates, Padumasūriyavaṃśa has been identified with figures mentioned in 17th-century European accounts of Siam, notably Du Royaume de Siam and the Instructions Given to the Siamese Envoys Sent to Portugal in 1684,^{[7]: 38 [12]: 127} which date his enthronement to 757 CE.^[8] On this basis, Ketumāla's reign is inferred to have concluded in that year.

The Ayutthaya Testimonies provide a more geographically specific reference, stating that Indapraṣṭhanagara lay east of Sankhaburi in the Phraek Si Racha historical region.^[2]: 4–5 The city is further described as having existed prior to the reign of Padumasūriyavaṃśa,^[2]: 6 which is said to have begun in 757 CE.^[a] This area broadly corresponds to the central Menam Basin and the Si Thep zone. However, the Ratanabimbavaṃsa records that Adītaraj of Ayojjhapura—often identified with Si Thep^[13]—once launched a military campaign against Indapraṣṭhanagara at a time when the latter was suffering from a severe flood,^{[5]: 94 [13][14]: 51} while Lavo, also located east of Phraek Si Racha, is recorded as a tributary of Indapraṣṭhanagara in the Chronicle of Padumasuriyavamsa,^[3]: 8 thereby indicating that the three were distinct polities.^[13] This distinction supports the conclusion that Indapraṣṭhanagara was located somewhere within the Phraek Si Racha region.

The location described in the Ayutthaya Testimonies corresponds closely with that recorded in the Yonok Chronicle [th], which, in its account of the period associated with the legendary Yonok monarch Phrom (r. 1029–1089), states that Indapraṣṭhanagara was situated within the Chao Phraya Basin and possessed direct access to the sea.^[5]: 166

Indapraṣṭhanagara is again mentioned in the Legend of Nakhon Si Thammarat [th]. This account states that Sri Dharmasokaraja I, identified as king of Indapraṣṭhanagara, fled southward, in 1117, with his brother Candrabhānu I (Sri Dharmasokaraja II)^[d] and his son Vaṃśasurā I (Sri Dharmasokaraja III) due to severe endemic disease and demographic decline in the royal city.^[4]: 37 Sri Dharmasokaraja I is said to have re-founded Nakhon Si Thammarat as his new seat of power.^{[4]: 37 [16]: 28}

This narrative is supported by the Dong Mè Nang Mưo’ng Inscription (K. 766), discovered north of the Phraek Si Racha region in modern Nakhon Sawan Province and dated to 1167 CE. The inscription records Sri Dharmasokaraja I as deceased and indicates the succession of Sri Dharmasokaraja II.^{[4]: 38 [15]} Together, the interpretation on both sources suggest that Sri Dharmasokaraja II may have attempted to reclaim the former northern territories, particularly the Phraek Si Racha and Lavo regions, of his father,^[4]: 40 reinforcing the hypothesis that Indapraṣṭhanagara lay in Phraek Si Racha.

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Earlier Thai historiography frequently equated Indapraṣṭhanagara with Angkorian Yaśodharapura,^[3][5]: 94 placing the Padumasūriyavaṃśa narrative within the Khmer chronicle tradition.^[3][5]: 42 However, the inferred date of 757 CE for the reign of Padumasūriyavaṃśa^[a] predates the conventional foundation of Yaśodharapura in the late 9th century by nearly two centuries.^[c] This chronological discrepancy, together with references to a fragmented political landscape in the Tonlé Sap basin during the 8th century,^[17]: 6 thereby standing in marked contrast to Thai textual narratives that depict the reign of Padmasūryavaṁśa as an era of territorial consolidation in which multiple polities were brought under his control, including Lavo, Sukhothai, and Talung (เมืองตลุง or ตะลุมดอ).^[3]: 8 These undermines the Angkor identification. Moreover, narratives associated with the Legend of Phra Ruang, as preserved in the Northern Chronicle and recounting the enthronement of the legendary Sricandradhipati in 959 CE, refer explicitly to Angkor as Mueang Kamphucha Thibodi (เมืองกัมพูชาธิบดี; lit. 'the royal city of the Kampuchea king'), rather than as Indapraṣṭhanagara,^{[18]: 27–9} whose existence is described as continuing into the early 13th century.^[b]

An alternative interpretation situates Indapraṣṭhanagara in the Phraek Si Racha region, east of Sankhaburi, which accords with the location provided in the Ayutthaya Testimonies^[2]: 5–6 and the narratives surrounding Sri Dharmasokaraja I and his son Sri Dharmasokaraja II.^[4]: 37 Under this view, Indapraṣṭhanagara probably emerges as a central Menam Basin polity that predated and later interacted with both Angkorian and Sukhothai powers.

Re-locating Indapraṣṭhanagara to the Phraek Si Racha region substantially reshapes interpretations of political developments in the late 12th and early 13th centuries. According to the Ayutthaya Testimonies, Sukhothai had long functioned as a tributary polity of Indapraṣṭhanagara, with tribute obligations reportedly maintained since the reign of Padumasūriyavaṃśa.^[3]: 8 The termination of these payments during the reign of Candraraja (r. 1184–1214) marked a rupture in the established political order and precipitated a confrontation that ultimately resulted in Sukhothai’s de facto independence.^{[2]: 15–6} In this period, Phraek Si Racha corresponds to the re-established polity known as Chen Li Fu,^{[19]: 9, 15 [20]: 20–3} which existed between approximately 1180 and the early 13th century.^{[21]: 1–6} The period of conflict with Sukhothai coincides with the reign of Se-li-Mo-hsi-t’o-pa-lo-hung or Mahīdhāravarman III, whose reign began in 1204/05.^[21]: 7

This reinterpretation also has significant implications for dynastic history. The royal houses of Indapraṣṭhanagara and Sukhothai are described in Ayutthaya Testimonies as belonging to the same lineage,^{[2]: 16–7} while the earlier rulers of the Menam valleys—the Xiū Luó Fēn line—are identified as progenitors of both the Sukhothai and Ayutthaya dynasties.^[e] Moreover, the rulers of Chen Li Fu (Indapraṣṭhanagara) have been tentatively associated with Phimai and the Angkorian Mahidharapura lineage.^[19]: 6 Under this framework, Sukhothai, Ayutthaya, Angkor, and Indapraṣṭhanagara (identified with Xiū Luó Fēn and later Chen Li Fu) emerge not as isolated or antagonistic polities but as interconnected entities linked through dynastic alliances.

These proposed dynastic relationships also illuminate accounts of the defeats suffered by Xiū Luó Fēn rulers at the hands of Sri Dharmasokaraja II in 1157 (in the Lavo region) and again in 1167 (in the Phraek Si Racha region). During this period, two Xiū Luó Fēn princes are recorded as retreating northward into the upper Menam basin. Suryaraja, identified as the grandfather of Si Intharathit, established authority in the area of modern Kamphaeng Phet,^[2]: 11 while Pra Poa Noome Thele Seri consolidated power in the Sukhothai–Nakhon Thai region.^{[8][12]: 127} These movements form part of the longue durée processes that culminated in the emergence of the Sukhothai Kingdom in the 13th century. Following the decline of Xiū Luó Fēn authority, Angkor under Jayavarman VII intervened militarily and successfully captured Lavo in 1180.^[4]: 39 In the same year, another ruling house—likely connected to the Mahidharapura dynasty^[19]: 6—seized control of Phraek Si Racha from Sri Dharmasokaraja II and re-established the polity as Chen Li Fu.^[21]: 18 This sequence of events may be interpreted as a strategic effort to reclaim or stabilize allied territories within the Menam basin. Moreover, in that same year, Pra Poa Noome Thele Seri—whose paternal territory had previously been lost to Sri Dharmasokaraja II—is recorded in the Legend of Nakhon Si Thammarat as having attempted to invade Tambralinga, which by that time constituted the only remaining dominion of Sri Dharmasokaraja II following his defeat in the Menam Basin by Angkor.^[4]: 41

Evidence for such alliances is further suggested by the recorded marriage between Pha Mueang of Sukhothai and Princess Sukhara Mahādevī, a relative of the Angkorian monarch Jayavarman VII,^[23] by depictions of Xiān (Siamese) mercenaries in Angkor Wat reliefs,^[24]: 70 and by the presence of large numbers of Siamese people in the Angkorian capital of Yasodharapura in the 13th century, as recorded by the Chinese envoy Zhou Daguan.^[25][26] Within this interpretive framework, figures such as Khom Sabat Khlon Lamphong—previously portrayed as Angkorian officials who usurped Sri Naw Nam Thum of Sukhothai—may instead represent rival ruler aligned with a competing political faction rather than agent of Angkor. This interpretation aligns with recent scholarship, which suggests that the early polities of Sukhothai and Angkor were linked through dynastic alliances rather than characterized by the rivalry traditionally assumed in earlier historiography.^{[27]: 58 [28]}

Finally, the identification of Indapraṣṭhanagara with Phraek Si Racha, together with evidence for dynastic connections between Siamese and Angkorian monarchs, lends support to an alternative version of the Legend of Nakhon Si Thammarat [th], which explicitly portrays Sri Dharmasokaraja I—the father of Sri Dharmasokaraja II—as a foreign monarch who exercised political authority over the Phraek Si Racha–Lavo region prior to his relocation southward.^[4]: 37 According to the legend, Sri Dharmasokaraja I, whose origins are traced to Hanthawaddy^[16]: 28 under Pagan suzerainty at the time,^[29]: 33 established a royal center at Indapraṣṭhanagara and ruled the surrounding Menam basin.^{[4]: 37–40 [16]: 28} The narrative further relates that, following a severe epidemic in 1117, he abandoned Indapraṣṭhanagara and transferred his power base to Nakhon Si Thammarat.^[4]: 37 This Pagan invasion corresponds closely with descriptions in the Northern Chronicle concerning the events during the late Dvaravati, including the expansion of Pagan influence into the Menam basin during the period from 1050s to 1080s, the establishment of Pagan noble Kar Tayy authority in Suphannaphum,^[18]: 60 and the reported invasion of Ayodhya in 1087, which resulted in the death of King Narai I^{[18]: 40–2 [30]} and a subsequent two-year interregnum before the accession of Phra Chao Luang, a ruler of uncertain origin.^{[18]: 41–2} The reported northward relocation of the Xiū Luó Fēn ruler Surindraraja (r. 1062–1100) from Phraek Si Racha to Chai Nat during this same period^[2]: 41 further reinforces the interpretation of these developments as interconnected consequences of regional upheaval and external intervention. These narratives align with Burmese historiographical traditions, which record that during the reign of Anawrahta of Pagan (r. 1044–1077), Pagan engaged in a series of military conflicts with Angkor and is even said, in some accounts, to have temporarily seized Angkor itself.^[29]: 34 They further accord with the scholarly interpretation that the phase of Tambralinga corresponding to the reign of Sri Dharmasokaraja I, followed by those of his successors—Sri Dharmasokaraja II and Sri Dharmasokaraja III—likely represented a period of Pagan suzerainty over Tambralinga, extending from the mid-11th century to the early 13th century.^{[31]: 89–90 [32]: 61}