An ancient Greek portico is a structure that was used as an entrance or walkway. The two most common types of porticos were the STOA and the xyst. A STOA was a long, covered colonnade with an open-air courtyard in the center. It was typically used for public gatherings and markets. A xyst was a long, narrow, open-air portico used for exercise and athletic training. Both the STOA and the xyst were popular in Ancient Greece and were often found in public spaces.