What is strie, you ask? Before rollers and latex, paint was a thick emulsion that went on with tedious brushing. Bristle marks were often visible, and they became more prominent as years and dirt accumulated. The strie technique mimics the look of centuries-old paint altered by dust and sun. In other words, it's a really cool paint effect. You should try it.
For full step-by-step instructions, see Decorative Painting Techniques: Strie