Fire on the Hills: How Fast Could the Armada Beacons Carry the News?

When the Spanish Armada was sighted off the Lizard in July 1588, a chain of beacons spread the warning across England. Many hills still carry the word "beacon" in their names. I use those names to ask how fast fire could have carried the news. From the Ordnance Survey's open gazetteer I take 193 hills and summits named for a beacon and trace lines of sight between every pair over a 90 m elevation model, with earth curvature and refraction, from a watcher 2 m above the ground to a fire 5 m above it. Within 50 km, 85% of sites can see another site's fire, but the sites split into 44 separate networks; the largest holds 65. A fire lit at the site nearest the Lizard reaches only 12 sites, all in Cornwall, and no chain of beacon names reaches London, York or Berwick even with sight lines of 150 km. Adding one possible relay hill per 10 km square, the fire reaches the edge of London in 9 hops and 191 of the 193 beacon sites within 18 hops. At an assumed 5, 15 or 30 minutes a hop, London is 45 minutes, 2 hours 15 minutes or 4 hours 30 minutes from the Lizard. Only three relay hills are needed to join the named beacons from the Lizard to London. The names are evidence of where fires were lit at some time, not a register of the 1588 chain, but they come close to a working network. Interactive version: https://tristan-hotham.github.io/armada-beacons/. Data and code: https://github.com/Tristan-Hotham/armada-beacons. Blog post: https://blog.tristanhotham.com/2026/10/27/armada-beacons/.