enduringly
In a way that lasts a very long time.
Enduringly means in a way that lasts for a long time or persists through difficulties. When something happens enduringly, it doesn't fade away quickly or fall apart when things get tough.
Some friendships are enduringly strong, staying close through years of change, distance, and life's ups and downs. Classic books like Charlotte's Web or The Lion, the Witch and the Wardrobe remain enduringly popular because each new generation of readers loves them just as much as the last. The Great Pyramid of Giza has stood enduringly for over 4,500 years, weathering sandstorms, earthquakes, and the passage of countless centuries.
Something that happens enduringly has staying power. A scientist might work enduringly on a problem for decades before solving it. A tree planted today might grow enduringly, providing shade for your great-grandchildren.
When you do something enduringly, you're in it for the long haul. You're not looking for quick success that disappears tomorrow. You're building something meant to last.