Indian intelligence officials state that China had been carrying out a steady military build-up in the Chumbi Valley, building many garrisons and converting the valley into a strong military base. In 1967, border clashes occurred at Nathu La and Cho La passes, when the Chinese contested the Indian demarcations of the border on the Dongkya range. In the ensuing artillery fire, states scholar Taylor Fravel, many Chinese fortifications were destroyed as the Indians controlled the high ground. In fact, the Chinese military is believed to be in a weak position in the Chumbi Valley because the Indian and Bhutanese forces control the heights surrounding the valley.