Base rnd, each side: Multiple of 10 + 1 + corner sts.
Begin 1 st to left of corner st.
Rnd 1: Ch 3 (counts as dc), *[dc in next st, ch 2, skip 2 sts, dc in next 2 sts] to corner st, (dc, ch 3, dc) in corner st**, dc in next st; rep from * around, ending last rep at **, join with slip st to top of ch-3.
Rnd 2: Ch 3 (counts as dc), dc in each dc and 2 dc in each ch-2 space around, placing 7 dc in each ch-3 corner space, join with slip st to top of ch-3.
Rnd 3: Ch 1, sc in each dc around, placing 3 sc in each corner st, join with slip st to first sc.
Rnd 4: Ch 1, Spike sc in same st 2 rows below, sc in next sc, *[Spike sc in next st 2 rows below, sc in next sc]** to corner st, (Spike sc, sc, Spike sc) in corner st, sc in next sc; rep from * around, ending last rep at **, join with slip st to first sc. Fasten off.