Tilbury Fort was constructed in the late 17th century, and replaced a smaller blockhouse built during the reign of Henry VIII. Artillery was now the dominant weapon and the fort was designed to withstand an artillery bombardment, built low lying with earth embankments fronted by brick. The heaviest guns were mounted along the river bank to protect the Thames from hostile shipping. The landward side was defended by a double line of moats that kept enemy guns at a distance, and brick revetted bastions at the corners of the fort that allowed its own guns to provide complete covering fire in front of the walls. This style of fortification, known as the bastion system, was popular in Europe at the time, and Tilbury remains the best preserved example in Britain. Unfortunately this is best seen from above, but aerial photographs exhibited at the fort show the defences clearly.