Here's the order in which they take place:
1. Temple of Doom (1984) - This movie is a prequel to Raiders and takes place in 1935.
2. Raiders of the Lost Ark (1981) - This movie takes place in 1936, directly following Temple of Doom.
3. The Last Crusade (1989) - This movie takes place in 1938.
So, if you want to watch the original trilogy in chronological order, you should start with Temple of Doom .