The flag of Tonga consists of a red field with a white canton charged with a red couped cross. Adopted in 1875 after being officially enshrined into the nation's constitution, it has been the flag of the Kingdom of Tonga since that year.

The constitution stipulates that the national flag can never be changed. The colours and symbols of the flag carry cultural, political, and regional meanings. The red couped cross alludes to Christianity, the religion practised by approximately 97% of the country's population. The white epitomises purity, while the red evokes the sacrifice of the Blood of Christ, which he shed during his Crucifixion. Wikipedia