Complex sentence: Upon its capture, further construction work began, and eventually the town was besieged from all sides By a fleet of small boats, which they brought down from the river Svir through Lake Ladoga, they succeeded in completely blockading the fort.
Split into simpler sentences: Upon its capture, further construction work began, and eventually the town was besieged from all sides. Using a fleet of small boats, which they brought down from the river Svir through Lake Ladoga, they succeeded in completely blockading the fort.