Locals and tourists alike are likely to have colorful memories of San Antonio’s historic Market Square in central downtown. South Texas native Edna Campos Gravenhorst has released a book delving into the history and significance of the 210’s “El Mercado,” titled San Antonio’s Historic Market Square. She’s an established author and certified San Antonio tourism ambassador (so basically, she knows her stuff). As the book informs the reader, San Antonio’s founding in 1718 prompted a demand for plazas with businesses and parks. The city’s growth meant relocating the established markets, eventually giving way to a farmers market that developed into the Market Square we now know for its shops, tourist stops and late-night bites at Mi Tierra. Gravenhorst will be signing copies of her book and giving a presentation this week at The Twig Book Shop.