Boston’s Grand Boulevard, Commonwealth Avenue, provides one of the city’s most enduring popular strolls.  This Boston By Foot tour on Thursday, May 21 at 6 pm parallels the 19th-century filling and development of the Back Bay from its origin at Arlington Street.  The avenue and its promenade were planned to elegantly complement the transformation of the newly filled Back Bay, which was designed as an upscale neighborhood.  Meet your guide at the George Washington Statue in the Public Garden, at the corner of Arlington Street and Commonwealth Avenue.  $15 per person, $5 for Boston By Foot members.  Contact info@bostonbyfoot.org for more information, or call them at 617-367-2345.