Throughout the Far East you will find gateways with guardian lions. The original purpose of these statues seems to be lost in antiquity. Perhaps, they were there to keep away evil spirits, perhaps they were there to frighten off burglars. In Thailand we find various alternatives to lions. There are the famous giants (Yak) in the King's palace complex in Bangkok and in Chiang Mai we find one temple gate is guarded by giant cockerels.
The guardians at Wat Plaeng Har are like nothing else. These giant sphinx are really scary. If their purpose is to frighten people away, they would seem to be succeeding. There appears to be few visitors to this Wat. The Bot is locked up and construction work abandoned. However, there is an alternative explanation. The nearby Doi Tao lake has dried up, the market is deserted and Wat Plaeng Har now stands on a road to nowhere.