In riding along the south coast of England you may have noticed the old Martello towers in constant succession very near to each other. They are the result of an old scheme of protecting the coast from our ancient enemies.
It was supposed that as soon as ever a French ship was seen in the distance the beacon would be fired at the Martello tower, and then, across old England, wherever her sons dwelt, there would flash the fiery signal news that the enemy was at hand, and every man would seize the weapon that was next to him to dash the invader from the shore.
Now, we need that the Church of Christ should be guarded with Martello towers of sacred watchers, who shall day and night look out for the attack of the enemy. For the enemy will come; if he come not when we are prayerless, he will surely come when we are prayerful. He will show the cloven hoof as soon as ever we show the bended knee.
Watch in Prayer
If our motto be "Prayer," his watchword will be "Fierce attack." Watch, then, while ye continue in prayer.
Source: C. H. Spurgeon