Norman Arch Crochet stitch.

Foundation:
Chain a multiple of 9 + 1, then add 1 extra chain for turning. (Example: 38 chains.)

Row 1 (WS):
1 double crochet (dc) into 2nd chain from hook.
*3 chains, skip 3 chains, 1 dc into next chain, 7 chains, 1 dc into next chain, skip 3 chains, 1 dc into next chain; repeat from * to end.

Row 2:
Chain 1, 1 dc into first dc, skip 3 chains, work 13 treble crochets (tr) into next 7-chain arch, skip 3 chains, 1 dc into next dc; repeat across, skipping turning chain at the end, turn.

Row 3:
Chain 3 (counts as first treble crochet), skip first dc and next 5 tr, *(1 tr into next tr, 3 chains) twice, 1 tr into next tr, skip next 5 tr, 1 dc among 5 tr; repeat from * ending last repeat at **, skip next 5 tr, 1 tr into last dc, skip turning chain, turn.

Row 4:
Chain 4 (counts as 1 tr), skip first stitch and next tr, 1 tr into next chain, 1 chain, skip chain, 1 tr into next chain, 3 chains, skip 1 tr, 1 tr into next chain, 1 chain, skip 1 chain, 1 tr into next chain, skip next 2 tr; repeat across, ending last repeat, skip next tr, 1 tr into top of turning chain, turn.

Row 5:
Chain 4 (counts as 1 tr + 3 chains), skip next 1-chain space, work (1 dc, 7 chains, 1 dc) into next 3-chain space, 3 chains, skip next 1-chain space, 1 tr between next 2 tr; repeat from * across, ending last repeat at **, 1 tr into top of turning chain, turn.

Pattern Repeat:
Repeat Rows 2–5 to continue the pattern.