The WRG rules for ancient wargaming were the first comprehensive set of wargaming rules suitable for national competitions amongst hobbyists. They were detailed by today's standards, needed 100+ figures a side and included the innovation of reaction tests; players found their troops did not always do what they expected them to (a bit like military history).
Out of print for many years, I brought them back into print and combined them with a guide to ancient warfare by Phil Barker, the man who wrote the original rules. The reprint sold a handful per month... until recently. Now a surge in sales indicates that many wargamers are bringing these rules out of retirement.
This renewed interest is a surprise to me, as it will be to most wargamers. The WRG 6th edition rules are a detailed simulation of ancient warfare, probably the most heavily playtested manual wargame in the world. Battles on the table top, with players using historical tactics, normally produce historically valid results.
The unexpected rise of WRG 6th edition ancients has reminded me that is almost impossible to predict sales trends in the world of wargaming.