Wat Pho Chai (Rang) is a not restored ruin located within the Portuguese settlement, off the city island in the southern area at present Samphao Lom Sub-district (1). The name of the temple could be translated as the Monastery of the Victorious Bodhi Tree; "Rang" stands for "vacated". The monastery is located south of Wat Phraya Phan.
The ruins were thought by quite a few scholars to be the location of the Portuguese Jesuit Church of San Paolo, until excavations performed by the Fine Arts Department in 2008, concluded it must have been a Buddhist monastic site. 
Historical data about the monastery and the exact time of its construction are unknown Excavations resulted in the findings of a number of small Buddha images and pieces from the boundary stones (sema) dating from the Late Ayutthaya period (1629 - 1767). 
Other discoveries, as for example pieces of a small bottle dating back to the Southern Song Dynasty (1127-1279), indicate that prior the arrival of the Portuguese in this area, the location was already inhabited by an ancient local community, predating the Ayutthaya-era. 
The site is not indicated on Phraya Boran Rachathanin's map of 1926, as the latter positioned Wat Portukes Yesuwid Nikai (Monastery of the Portuguese Jesuit Sect) along the Chao Phraya River (former old Lopburi River). The exact location of this Jesuit Church has not been discovered as yet.
The ruin of Wat Pho Chai is located in Geo. Coord.: 14° 19' 39.80" N, 100° 34' 16.20" E.
(1) Free translated the "Capsized Junk" sub-district.