Exerpted from the biography of the Venerable Ajahn Tate Khantipalo by Thanissaro Bhikkhu:
Since the time of the Buddha, more than two thousand five hundred years ago, monks have retreated into the depths of the forests, mountains and caves, seeking physical isolation to aid them in the development of meditation and realization of Dhamma, the truth of the Buddha's Teaching. Whether in solitude or in small groups, such monks live a life of simplicity, austerity and determined effort and have included some of the greatest meditation masters since the Buddha himself. Far from cities and towns, willing to put up with the rigours and hardships of living in the wild for the opportunity to learn from nature, and uninterested in worldly fame or recognition, these forest monks often remain unknown, their life stories lost among the jungle thickets and mountain tops.
The revival of the forest tradition in Thailand during the last century was a grassroots movement to return to the lifestyle and training that was practiced in the time of the Buddha. Some monks abandoned the busy village and town monasteries for the peace and quiet of the forest. They followed the Vinaya Rule more strictly, emphasizing the importance of every detail. Such monks lived without money, living frugally on whatever was offered and patiently enduring when necessities were scarce. They integrated the extra austere practices (tudong) recommended by the Buddha into their lifestyle. For example, eating only one meal a day from their alms bowl, wearing robes made from discarded cloth, and living in the forest or in cemeteries — often using a krot (a 'tent-umbrella' with mosquito net) for shelter. These forest monks would often wander barefoot through the sparsely settled regions — Thailand's previously small population was scattered over quite a large country — seeking places conducive to meditation.
The very heart of the forest tradition is the development of meditation. By cultivating deep states of tranquillity and systematically investigating the body and mind, insight can arise into the true nature of existence. The forest masters were noted for their creativity in overcoming the problems, hindrances and defilements of the mind, and for their daring determination to realize Nibbana, enlightenment, the fulfillment of the spiritual path taught by the Buddha.