Hundreds of flowers will forever illuminate Martin Place, the site of Sydney's worst terrorist attack, in a permanent memorial focused on how a city healed itself and defied fear.

The flowers laid by city workers on the morning of Tuesday, December 16 last year, as a shocked Sydney woke to the news that two hostages had died in the night, grew into a sea of bouquets.

Flower stalls ran dry as the people of Sydney solemnly queued to pay their respects to Katrina Dawson and Tori Johnson, filing slowly around an impromptu memorial that swelled to fill a block of Martin Place.

Premier Mike Baird will announce on Sunday that the design chosen for the permanent memorial to the Lindt Cafe siege will feature 400 flower symbols inlaid into the granite pavement of Martin Place.