Complex sentence: Following the signing of the treaty, construction was once again begun on the site in 1844, replacing the aborted 1812 era construction with a massive 3rd system masonary fortification known as Fort Montgomery.
Split into simpler sentences: Following the signing of the treaty, construction was resumed on the site. The new effort replaced the aborted 1812-era construction with a massive third-system masonry fortification known as Fort Montgomery.