Wat Khao Tha Kradan

Cairns on the approach road.

Reasons why people might build cairns on the entrance road to a temple:

To mark the entrance to the sacred space. A cairn at the entrance to a temple can serve as a visual cue that one is entering a special place. This can be especially important in temples that are located in remote or difficult-to-reach areas.
To offer respect to the deities or spirits associated with the temple. Building a cairn is a traditional way of making an offering to the spirits of nature, and many temples are believed to be inhabited by various deities. By building a cairn at the entrance to the temple, visitors can show their respect and ask for blessings.
To protect the temple from negative energy. Some people believe that cairns can help to protect sacred spaces from negative energy. By building a cairn at the entrance to a temple, visitors can help to create a positive and protective barrier around the site.
To mark a pilgrimage path. In some cultures, cairns are used to mark pilgrimage paths to holy sites. If a temple is located at the end of a pilgrimage route, building a cairn at the entrance can be a way to commemorate the journey and to show one's dedication to their faith.