Paul Revere is coming to Medford Square on Monday to celebrate Patriots Day. A costumed rider on horseback will recreate Revere’s historic midnight ride from Boston to Lexington, which took place on April 18-19, 1775. Festivities will begin at 10 a.m. in City Hall, where Mayor Michael J. McGlynn will join military veterans from Medford for a flag-raising ceremony. At 10:15 a.m., a memorial observance will be held at the Old Burial Ground on Salem Street. At 10:45, Paul Revere is due to stop at the historic Isaac Hall House at 43 High St. The house, now the site of the Gaffey Funeral Home, was once the home of a commander of the Medford Minutemen.