This chapter analzyes the collective thinking about Mars that has been shaped by two centuries of gradually improving astronomical observations of the red planet. It mentions several generations of astronomers that used their increasingly powerful telescopes to map the surface of Mars from the late seventeenth century into the mid-nineteenth century. It also talks about astronomers of recent centuries that believed they were discovering clues at the far ends of their telescopes that revealed Mars was likely the home of Martians. The chapter discusses the international community of astronomers that undertook a decades-long effort to map the Martian globe after they had determined that Mars shared intriguing similarities with Earth. It highlights the ongoing twentieth- and twenty-first-century searches for evidence of life on Mars as the indirect legacy of Giovanni Schiaparelli's discoveries and of Percival Lowell's unfettered imagination and indefatigable efforts to promote his ideas about Mars to the public.