Lammas Day is an Anglo-Saxon harvest festival celebrated on 1st August. Its name comes from Old English hlaf, "loaf" and mæsse, "mass", and it may have been a day when loaves of bread made from the first corn were blessed. Much about the origins of Lammas is obscure, but it's a festival with a long, interesting, and somewhat unusual history.
Lammas appears just once in Old English poetry, in the beautiful calendar poem known as the Menologium. In the section for August, "Weed-month", this poem describes Lammas and the coming of autumn":
ymb seofon niht þæs sumere gebrihted
Weodmonað on tun; welhwær bringeð
hlafmæssan dæg. Swa þæs hærfest cymð
ymbe oðer swylc butan anre wanan,
wlitig, wæstmum hladen. Wela byð geywed
fægere on foldan.
And [after the feast of St James] after seven nights
of summer's brightness Weed-month slips
into the dwellings; everywhere August brings
to peoples of the earth Lammas Day. So autumn comes, after that number of nights but one, bright, laden with fruits. Plenty is revealed, beautiful upon the earth.
I love the concept of August as "weed month" and, certainly this year, it does feel as if August is ushering in autumn, rather than being a summer month, full of sunshine, pimms and plants!