The iconic leftist revolutionary, who handed over power in 2008 to his younger brother Raul due to ill health, appeared later in the day for a birthday gala featuring children's theater, live music and videos from his life.
"I want to express my most profound gratitude for the shows of respect, the greetings and gifts I have received the days, which give me the strength to reciprocate through ideas," Castro wrote in the opinion piece.
"Fidel is the best thing that happened to our country," said Aldo Zamora, 40, selling candy-colored balloon animals at the street party along the Malecon, as a tropical electric storm lit up the night sky.