Complex sentence: Although the construction of the lighthouse was improved, still there was a danger that the light flowing out of it might be obscured by the growing trees, and construction of the first brick lighthouse began in 1806.
Split into simpler sentences: Although the construction of the lighthouse was improved, still there was a danger that the light flowing out of it might be obscured by the growing trees. That is why the construction of the first brick lighthouse began in 1806.