India and China fought a month-long war fifty years ago that did not resolve their mountainous border dispute. Since then, the two Asian rivals have found many ways of reminding each other about the frozen state of their disagreement.

In the latest row, their quarrel over each country’s maps actually shows up on the images of their passports and visas.

Beijing recently began issuing new e-passports showing watermarks of two regions -- the Indian state of Arunachal Pradesh that China claims and the disputed Aksai Chin that China occupies -- as Chinese territory

That did not go down well in New Delhi.

Now, the Indian Embassy in Beijing is doing a tit-for-tat with its own map. It has started stamping its version of the Indian map on visas issued to Chinese citizens, one that includes the two regions.

However, India is not the only nation upset by the new Chinese passports: They also show images of the disputed, resource-rich islands in the South China Sea as Chinese territory, islands that Vietnam and the Philippines also claim.

Despite a series of continuing and cordial talks between Beijing and New Delhi, during which they have even exchanged their respective ground maps, relations between the two countries remain strained.

This is not the first time that India and China, who share about 2,400 miles of border, have squabbled over maps and passports.

Two years ago, China caused much irritation among Indian officials when it began stapling the visas of residents of Kashmir, a Himalayan province where Indian troops are fighting to put down a Pakistan-backed separatist Islamist insurgency for more than two decades. By stapling the visas, instead of stamping them, Beijing was declaring that they regarded Kashmir was a disputed region as well.

Indian officials had to sternly remind Beijing in 2010 to be “sensitive” to its concerns about Kashmir, just as New Delhi is sensitive to Beijing’s attitude about Tibet.

Earlier this year, Beijing declined to issue a visa to an Indian air force officer who hails from Arunachal Pradesh. The row led New Delhi to cut the size of the military delegation that visited China in January.